Fluoropolymer produced by aqueous polymerization using dispersed particulate of fluorinated ionomer

ABSTRACT

A process for making an aqueous dispersion of fluoropolymer particles by providing dispersed particulate of fluorinated ionomer in an aqueous polymerization medium and polymerizing at least one fluorinated monomer in the aqueous polymerization medium in the presence of the dispersed particulate of fluorinated ionomer and initiator to form the aqueous dispersion of particles of fluoropolymer.

FIELD OF THE INVENTION

This invention relates to a process for the dispersion polymerization offluorinated monomer in an aqueous polymerization medium andfluoropolymer particles and aqueous dispersions made thereby.

BACKGROUND OF THE INVENTION

A typical process for the aqueous dispersion polymerization offluorinated monomer includes feeding fluorinated monomer to a heatedreactor containing a fluorosurfactant and deionized water. Paraffin waxis employed in the reactor as a stabilizer for some polymerizations,e.g., polytetrafluoroethylene (PTFE) homopolymers. A free-radicalinitiator solution is employed and, as the polymerization proceeds,additional fluorinated monomer is added to maintain the pressure. Achain transfer agent is employed in the polymerization of some polymers,e.g., melt-processible TFE copolymers, to control melt viscosity. Afterseveral hours, the feeds are stopped, the reactor is vented and purgedwith nitrogen, and the raw dispersion in the vessel is transferred to acooling vessel.

For use in fluoropolymer coatings for metals, glass and fabric, polymerdispersion is typically transferred to a dispersion concentrationoperation which produces stabilized dispersions used as coatings.Certain grades of PTFE dispersion are made for the production of finepowder. For this use, the polymer dispersion is coagulated, the aqueousmedium is removed and the PTFE is dried to produce fine powder.Dispersions of melt-processible fluoropolymers for molding resin arealso coagulated and the coagulated polymer dried and then processed intoa convenient form such as flake, chip or pellet for use in subsequentmelt-processing operations.

As described in U.S. Pat. No. 3,391,099 to Punderson, dispersionpolymerization involves two generally distinct phases. The initialperiod of the reaction is a nucleation phase in which a given number ofpolymerization sites or nuclei are established. Subsequently, thereoccurs a growth phase in which polymerization of fluorinated monomer onestablished particles occurs with little or no formation of newparticles. Successful production of the high solids fluoropolymerdispersion generally requires the presence of the fluorosurfactant.

Fluorosurfactants used in the polymerization are usually anionic,non-telogenic, soluble in water and stable to reaction conditions. Themost widely used fluorosurfactants are perfluoroalkane carboxylic acidsand salts as disclosed in U.S. Pat. No. 2,559,752 to Berry, specificallyperfluorooctanoic acid and salts, often referred to as C8, andperfluorononanoic acid and salts, often referred to as C9. Because ofrecent environmental concerns with regard to perfluorooctanoic acid andsalts, there is interest in reducing or eliminating perfluoroalkanecarboxylic acids and their salts in fluoropolymer polymerizationprocesses.

SUMMARY OF THE INVENTION

The invention is based on the discovery that a process for making anaqueous dispersion of fluoropolymer particles is effectively carried outby providing dispersed particulate of fluorinated ionomer in an aqueouspolymerization medium and polymerizing at least one fluorinated monomerin the aqueous polymerization medium in the presence of the dispersedparticulate of fluorinated ionomer and initiator to form the aqueousdispersion of particles of fluoropolymer.

In one preferred form of the present invention, the amount of dispersedparticulate of fluorinated ionomer provided in the aqueouspolymerization medium comprises less than about 15 wt % of thefluoropolymer solids produced in the aqueous dispersion. In anotherpreferred form of the invention, the dispersed particulate offluorinated ionomer has a weight average particle size of about 2 nm toabout 100 nm. The fluorinated ionomer preferably has an ion exchangeratio of about 3 to about 53. In a preferred embodiment of theinvention, the fluorinated ionomer is highly fluorinated, morepreferably, perfluorinated.

In a preferred form of the invention, the process further comprisesproviding surfactant in said polymerization medium. Preferably, thesurfactant comprises fluorosurfactant, more preferably, fluoroethersurfactant.

DETAILED DESCRIPTION OF THE INVENTION Fluorinated Ionomer

Particulate of fluorinated ionomer is employed in the process inaccordance with the present invention. “Fluorinated Ionomer” means afluoropolymer having sufficient ionic groups to provide an ion exchangeratio of no greater than about 53. In this application, “ion exchangeratio” or “IXR” is defined as number of carbon atoms in the polymerbackbone in relation to the ionic groups. Precursor groups such as —SO₂Fwhich upon hydrolysis become ionic are not treated as ionic groups forthe purposes of determining IXR. The fluorinated ionomer employed in theprocess of the invention preferably has an ion exchange ratio of about 3to about 53. More preferably, the IXR is about 3 to about 43, even morepreferably about 3 to about 33, still more preferably about 8 to about33, most preferably 8 to about 23. In a preferred embodiment, thefluorinated ionomer is highly fluorinated. “Highly fluorinated” inreference to ionomer means that at least 90% of the total number ofunivalent atoms bonded to carbon atoms in the polymer are fluorineatoms. Most preferably, the ionomer is perfluorinated.

In fluorinated ionomers, the ionic groups are typically distributedalong the polymer backbone. Preferably, the fluorinated ionomercomprises a polymer backbone with recurring side chains attached to thebackbone with the side chains carrying the ionic groups. Preferredfluorinated ionomer comprises ionic groups having a pKa less than about10, more preferably, less than about 7. Ionic groups of the polymer arepreferably selected from the group consisting of sulfonate, carboxylate,phosphonate, phosphate, and mixtures thereof. The terms “sulfonate,carboxylate, phosphonate and phosphate” are intended to refer to eitherthe respective salts or respective acids from which salts can be formed.Preferably, when salts are employed, the salts are alkali metal orammonium salts. Preferred ionic groups are sulfonate groups. Sulfonategroups in preferred fluorinated ionomers used in the process of theinvention have a pKa of about 1.9 as measured on the fluorinated ionomerin aqueous dispersion form having 10 wt % solids at room temperature.

Various known fluorinated ionomers can be used including polymers andcopolymers of trifluoroethylene, tetrafluoroethylene (TFE),α,β,β-trifluorostyrene, etc., into which ionic groups have beenintroduced. α,β,β-trifluorostyrene polymers useful for the practice ofthe invention are disclosed in U.S. Pat. No. 5,422,411. Possiblepolymers include homopolymers or copolymers of two or more monomers.Copolymers are typically formed from one monomer which is anonfunctional monomer and which provides carbon atoms for the polymerbackbone. A second monomer provides both carbon atoms for the polymerbackbone and also contributes the side chain carrying the ionic group orits precursor, e.g., a sulfonyl fluoride group (—SO₂F), which can besubsequently hydrolyzed to a sulfonate functional group. For example,copolymers of a first fluorinated vinyl monomer together with a secondfluorinated vinyl monomer having a sulfonyl fluoride group (—SO₂F) canbe used. Possible first monomers include tetrafluoroethylene (TFE),hexafluoropropylene, vinyl fluoride, vinylidine fluoride,trifluoroethylene, chlorotrifluoroethylene, perfluoro(alkyl vinylether), and mixtures thereof. Possible second monomers include a varietyof fluorinated vinyl ethers with ionic groups or precursor groups whichcan provide the desired side chain in the polymer. The first monomer mayalso have a side chain. Additional monomers can also be incorporatedinto these polymers if desired.

A class of preferred ionomers for use in the present invention includesa highly fluorinated, most preferably perfluorinated, carbon backboneand the side chain is represented by the formula—(O—CF₂CFR_(f))_(a)—(O—CF₂)_(b)—(CFR′_(f))_(c)SO₃X,wherein R_(f) and R′_(f) are independently selected from F, Cl or aperfluorinated alkyl group having 1 to 10 carbon atoms, a=0 to 2, b=0 to1, c=0 to 6, and X is H, Li, Na, K or NH₄. The preferred ionomersinclude, for example, polymers disclosed in U.S. Pat. Nos. 3,282,875 andin 4,358,545 and 4,940,525. One preferred ionomer comprises aperfluorocarbon backbone and the side chain is represented by theformula —O—CF₂CF(CF₃)—O—CF₂CF₂SO₃X, wherein X is as defined above.Ionomers of this type are disclosed in U.S. Pat. No. 3,282,875 and canbe made by copolymerization of tetrafluoroethylene (TFE) and theperfluorinated vinyl ether CF₂═CF—O—CF₂CF(CF₃)—O—CF₂CF₂SO₂F,perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) (PDMOF),followed by conversion to sulfonate groups by hydrolysis of the sulfonylfluoride groups and ion exchanging if needed to convert to the desiredform. One preferred ionomer of the type disclosed in U.S. Pat. Nos.4,358,545 and 4,940,525 has the side chain —O—CF₂CF₂SO₃X, wherein X isas defined above. This ionomer can be made by copolymerization oftetrafluoroethylene (TFE) and the perfluorinated vinyl etherCF₂═CF—OCF₂CF₂SO₂F, perfluoro(3-oxa-4-pentenesulfonyl fluoride) (POPF),followed by hydrolysis and acid exchange if needed.

For ionomers of this type, the cation exchange capacity of a polymer isoften expressed in terms of equivalent weight (EW). For the purposes ofthis application, equivalent weight (EW) is defined to be the weight ofthe ionomer in acid form required to neutralize one equivalent of NaOH.In the case of a sulfonate ionomer where the ionomer comprises aperfluorocarbon backbone and the side chain is—O—CF₂—CF(CF₃)—O—CF₂—CF₂—SO₃H (or a salt thereof), the equivalent weightrange which corresponds to an IXR of about 8 to about 23 is about 750 EWto about 1500 EW. IXR for this ionomer can be related to equivalentweight using the following formula: 50 IXR+344=EW. While generally thesame IXR range is used for sulfonate ionomers disclosed in U.S. Pat.Nos. 4,358,545 and 4,940,525, e.g., the ionomer having the side chain—O—CF₂CF₂SO₃H (or a salt thereof), the equivalent weight is somewhatlower because of the lower molecular weight of the monomer unitcontaining the ionic group. For the preferred IXR range of about 8 toabout 23, the corresponding equivalent weight range is about 575 EW toabout 1325 EW. IXR for this polymer can be related to equivalent weightusing the following formula: 50 IXR+178=EW.

The molecular weight of the fluorinated ionomer particulate cangenerally be in the same range as the resin which is used in ionexchange polymer membranes used in the chloralkali process for theelectrolytic production of chlorine and sodium hydroxide from sodiumchloride and in fuel cells. Such fluorinated ionomer resin has amolecular weight which preferably provides solid fluorinated ionomerparticulate at room temperature. In thermoplastic forms of thefluorinated ionomer, melt flow rate is preferably in the range of 1 toabout 500, more preferably about 5 to about 50, most preferably about 10to about 35 g/10 min.

The fluorinated ionomer particulate of the dispersion employed inaccordance with the process of the invention preferably has a weightaverage particle size of about 2 nm to about 100 nm. More preferably,such particulate has a weight average particle size of about 2 to about50 nm, even more preferably about 2 to about 30, still more preferablyabout 2 to about 10 nm. A suitable preparation method for aqueousdispersions of such fluorinated ionomer particulate is taught in U.S.Pat. Nos. 6,552,093 and 7,166,685 (Curtin et al.). The preparationmethod of Curtin et al. can provide “water only” aqueous dispersions.“Water only” means the aqueous dispersions contain a liquid medium whichcontains either no other liquids other than water or, if other liquidsare present, no more that about 1 wt %, of such liquids.

The weight average particle size in a liquid dispersion of fluorinatedionomer particulate used in accordance with the invention can bemeasured by a dynamic light scattering (DLS) technique as describedbelow in the Test Methods.

In accordance with the invention, dispersed fluorinated ionomerparticulate is preferably provided in the aqueous polymerization mediumby mixing a concentrated aqueous dispersion or dispersible powder of thefluorinated ionomer into the aqueous polymerization medium. Preferredconcentrated aqueous dispersions for use in accordance with theinvention are preferably the “water only” aqueous dispersions describedabout made as taught in U.S. Pat. Nos. 6,552,093 and 7,166,685 (Curtinet al.). Solids levels in such concentrates are preferably about 1 toabout 35 wt %, more preferably about 5 to about 35 wt %. Aqueousdispersions made as disclosed in U.S. Pat. Nos. 6,552,093 and 7,166,685B2 (Curtin et al.) can also be dried to form powders which are readilyredispersed in water or various polar organic solvents to providedispersions in such solvents. While dispersions of fluorinated ionomerparticulate in polar organic solvents may be useful in the practice ofthe invention, such solvents are usually telogenic and it is generallypreferred to employ aqueous dispersions of the fluorinated ionomer inthe practice of the present invention with low amounts or no organicsolvents present. Thus, dried powders of the dispersions made accordingto U.S. Pat. Nos. 6,552,093 and 7,166,685 B2 (Curtin et al.) can beintroduced directly into the aqueous polymerization medium or mixed withwater to produce a concentrated aqueous dispersion prior to suchintroduction to provide the dispersion of fluorinated ionomerparticulate. Concentrated aqueous dispersions, whether made directlyfrom the process as disclosed in U.S. Pat. Nos. 6,552,093 and 7,166,685B2 (Curtin et al.) or made from dried powders, can be produced andstored at concentrations up to 35 wt % solids, are stable for longperiods, and can be diluted to any desired concentration with water.

Suitable fluorinated ionomer dispersions may also be available in, forexample, mixed solvents of water and lower alcohols as disclosed in U.S.Pat. No. 4,443,082 (Grot). The alcohol content of such dispersions maybe reduced or substantially removed using, for example, a rotaryevaporator.

Fluoropolymer

“Fluoropolymer” means polymer polymerized from at least one fluorinatedmonomer and which polymer has no measureable ionic groups, or a limitednumber of ionic groups providing an ion exchange ratio of greater thanabout 53, i.e., is nonionomeric fluoropolymer. Precursor groups such as—SO₂F which upon hydrolysis become ionic are not treated as ionic groupsfor the purposes of determining IXR. Preferred fluoropolymers have noionic groups, or a limited number of ionic groups providing an ionexchange ratio of greater than about 100. The fluorinated monomer usedin the process of this invention is preferably independently selectedfrom the group consisting of tetrafluoroethylene (TFE),hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE),trifluoroethylene, hexafluoroisobutylene, perfluoroalkyl ethylene,fluorovinyl ethers, vinyl fluoride (VF), vinylidene fluoride (VF2),perfluoro-2,2-dimethyl-1,3-dioxole (PDD),perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD), perfluoro(allylvinyl ether) and perfluoro(butenyl vinyl ether). A preferredperfluoroalkyl ethylene monomer is perfluorobutyl ethylene (PFBE).Preferred fluorovinyl ethers include perfluoro(alkyl vinyl ether)monomers (PAVE) such as perfluoro(propyl vinyl ether) (PPVE),perfluoro(ethyl vinyl ether) (PEVE), and perfluoro(methyl vinyl ether)(PMVE). Non-fluorinated olefinic comonomers such as ethylene andpropylene can be copolymerized with fluorinated monomers.

Fluorovinyl ethers also include those useful for introducingfunctionality into fluoropolymers. In one embodiment of the invention,fluorovinyl ether monomers are employed in polymerization whichintroduce functional groups which are precursors for ionic groups. Theseinclude CF₂═CF—(O—F₂CFR_(f))_(a)—O—CF₂CFR′_(f)SO₂F, wherein R_(f) andR′_(f) are independently selected from F, Cl or a perfluorinated alkylgroup having 1 to 10 carbon atoms, a=0, 1 or 2. Polymers of this typeare disclosed in U.S. Pat. No. 3,282,875(CF₂═CF—O—CF₂CF(CF₃)—O—CF₂CF₂SO₂F,perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride)), and in U.S.Pat. Nos. 4,358,545 and 4,940,525 (CF₂═CF—O—CF₂CF₂SO₂F). Another exampleis CF₂═CF—O—CF₂—CF(CF₃)—O—CF₂CF₂CO₂CH₃, methyl ester ofperfluoro(4,7-dioxa-5-methyl-8-nonenecarboxylic acid), disclosed in U.S.Pat. No. 4,552,631. Functional groups in fluoropolymers incorporatingsuch monomers can be hydrolyzed by known methods after polymerization toform ionic groups. Although it is intended that the unhydrolyzed polymerbe considered a fluoropolymer for the purposes of polymerization inaccordance with the invention and within the scope of the claims, afterpolymerization such polymers may become fluorinated ionomer if uponhydrolysis such ionic groups are present in sufficient quantity toprovide an IXR of no greater than about 53. Other fluorovinyl etherswith functionality of nitrile, cyanate, carbamate, and phosphoric acidare disclosed in U.S. Pat. Nos. 5,637,748; 6,300,445; and 6,177,196.

The invention is especially useful when producing dispersions ofpolytetrafluoroethylene (PTFE) particles including modified PTFE. PTFEand modified PTFE typically have a melt creep viscosity of at leastabout 1×10⁸ Pa·s and, with such high melt viscosity, the polymer doesnot flow significantly in the molten state and therefore is not amelt-processible polymer. Polytetrafluoroethylene (PTFE) refers to thepolymerized tetrafluoroethylene by itself without any significantcomonomer present. Modified PTFE refers to copolymers of TFE with suchsmall concentrations of comonomer that the melting point of theresultant polymer is not substantially reduced below that of PTFE. Theconcentration of such comonomer is preferably less than 1 wt %, morepreferably less than 0.5 wt %. A minimum amount of at least about 0.05wt % is preferably used to have significant effect. The modified PTFEcontains a small amount of comonomer modifier which improves filmforming capability during baking (fusing), such as perfluoroolefin,notably hexafluoropropylene (HFP) or perfluoro(alkyl vinyl ether)(PAVE), where the alkyl group contains 1 to 5 carbon atoms, withperfluoro(ethyl vinyl ether) (PEVE) and perfluoro(propyl vinyl ether)(PPVE) being preferred. Chlorotrifluoroethylene (CTFE), perfluorobutylethylene (PFBE), or other monomer that introduces bulky side groups intothe molecule are also included.

The invention is especially useful when producing dispersions ofmelt-processible fluoropolymer particles. By melt-processible, it ismeant that the polymer can be processed in the molten state (i.e.,fabricated from the melt into shaped articles such as films, fibers, andtubes etc. that exhibit sufficient strength and toughness to be usefulfor their intended purpose) using conventional processing equipment suchas extruders and injection molding machines. Examples of suchmelt-processible fluoropolymers include homopolymers such aspolychlorotrifluoroethylene or copolymers of tetrafluoroethylene (TFE)and at least one fluorinated copolymerizable monomer (comonomer) presentin the polymer usually in sufficient amount to reduce the melting pointof the copolymer substantially below that of TFE homopolymer,polytetrafluoroethylene (PTFE), e.g., to a melting temperature nogreater than about 315° C.

A melt-processible TFE copolymer typically incorporates an amount ofcomonomer into the copolymer in order to provide a copolymer which has amelt flow rate (MFR) of about 1-100 g/10 min as measured according toASTM D-1238 at the temperature which is standard for the specificcopolymer. Preferably, the melt viscosity is at least about 10² Pa·s,more preferably, will range from about 10² Pa·s to about 10⁶ Pa·s, mostpreferably about 10³ to about 10⁵ Pa·s measured at 372° C. by the methodof ASTM D-1238 modified as described in U.S. Pat. No. 4,380,618.Additional melt-processible fluoropolymers are the copolymers ofethylene (E) or propylene (P) with TFE or CTFE, notably ETFE, ECTFE andPCTFE.

A preferred melt-processible copolymer formed in the practice of thepresent invention comprises at least about 60-98 wt %tetrafluoroethylene units and about 2-40 wt % of at least one othermonomer. Preferred comonomers with TFE are perfluoroolefin having 3 to 8carbon atoms, such as hexafluoropropylene (HFP), and/or perfluoro(alkylvinyl ether) (PAVE) in which the linear or branched alkyl group contains1 to 5 carbon atoms. Preferred PAVE monomers are those in which thealkyl group contains 1, 2, 3 or 4 carbon atoms, and the copolymer can bemade using several PAVE monomers. Preferred TFE copolymers include FEP(TFE/HFP copolymer), PFA (TFE/PAVE copolymer), TFE/HFP/PAVE wherein PAVEis PEVE and/or PPVE, MFA (TFE/PMVE/PAVE wherein the alkyl group of PAVEhas at least two carbon atoms) and THV (TFE/HFP/VF2).

Further useful polymers are film forming polymers of polyvinylidenefluoride (PVDF) and copolymers of vinylidene fluoride as well aspolyvinyl fluoride (PVF) and copolymers of vinyl fluoride.

The invention is also useful when producing dispersions of fluorocarbonelastomer particles. These elastomers typically have a glass transitiontemperature below 25° C. and exhibit little or no crystallinity, i.e.they are amorphous at room temperature. In one embodiment of the presentinvention, fluorocarbon elastomer copolymers made by of the processcontain 25 to 70 wt %, based on total weight of the fluorocarbonelastomer, of copolymerized units of a first fluorinated monomer whichmay be vinylidene fluoride (VF2) or tetrafluoroethylene (TFE) ormixtures thereof. The remaining units in the fluorocarbon elastomers arecomprised of one or more additional copolymerized monomers, differentfrom the first monomer, selected from the group consisting offluorinated monomers, hydrocarbon olefins and mixtures thereof.Fluorocarbon elastomers prepared by the process of the present inventionmay also, optionally, comprise units of one or more cure site monomers.When present, copolymerized cure site monomers are typically at a levelof 0.05 to 7 wt %, based on total weight of fluorocarbon elastomer.Examples of suitable cure site monomers include: i) bromine-, iodine-,or chlorine-containing fluorinated olefins or fluorinated vinyl ethers;ii) nitrile group-containing fluorinated olefins or fluorinated vinylethers; iii) perfluoro(2-phenoxypropyl vinyl ether); and iv)non-conjugated dienes.

Preferred TFE based fluorocarbon elastomer copolymers include TFE/PMVE,TFE/PMVE/E, TFE/P and TFE/P/VF2. Preferred VF2 based fluorocarbonelastomer copolymers include VF2/HFP, VF2/HFP/TFE, and VF2/PMVE/TFE. Anyof these elastomer copolymers may further comprise units of cure sitemonomer.

Surfactant

In addition to a dispersion of fluorinated ionomer particulate, theaqueous polymerization medium used to form the aqueous dispersion ofparticles of fluoropolymers may further comprise surfactant. Thesurfactant can be selected from a large group of suitable surfactantsincluding hydrocarbon surfactants, siloxane surfactants, andfluorosurfactants. Suitable hydrocarbon surfactants have been disclosedin U.S. Pat. No. 5,925,705 to Araki et al; and JP Patent Publications2004/358397 and 2004/359870 to Tsuda et al. Suitable siloxanesurfactants have been described in U.S. Pat. No. 6,841,616 to Wille etal. Preferably the surfactant is a fluorosurfactant and more preferablyis a fluoroether surfactant.

Examples of fluorosurfactants that may be a component of thepolymerization agent are described in U.S. Pat. No. 6,395,848 to Morganet al. as fluoroalkyl having at most one ether oxygen, preferablyperfluoroalkyl, carboxylic acids and salts thereof having 6-20 carbonatoms, preferably 6-12 carbon atoms, such as ammonium perfluorooctanoateand ammonium perfluorononanoate (see Berry, U.S. Pat. No. 2,559,752).Perfluoroalkyl sulfonic acids and salt may also be used. In oneembodiment of the invention, perfluoroalkyl ethane sulfonic acids andsalts thereof are employed, preferably a compound or a mixture ofcompounds of the formula F—(—CF₂—CF₂—)_(n)—CH₂CH₂—SO₃M, wherein n is 2-8and M is a cation having a valence of 1 as described in Khan & Morgan,U.S. Pat. No. 4,380,618. More preferably, such perfluoroalkyl ethanesulfonic acid surfactant comprises a compound of the formulaC₆F₁₃—CH₂CH₂—SO₃M, wherein M is a cation having a valence of 1 asdescribed in Baker & Zipfel, U.S. Pat. Nos. 5,688,884 and 5,789,508.Preferably, M in the above formula is NH₄ ⁺.

Additional examples of such fluorosurfactants include perfluoroalkoxybenzene sulfonic acids and salts thereof wherein the perfluoroalkylcomponent of the perfluoroalkoxy has 4-12 carbon atoms, preferably 7-12carbon atoms (as described in Morgan, U.S. Pat. No. 4,621,116).Additional examples of such surfactants also includepartially-fluorinated surfactants having internal methylene groups andhaving the formula R_(f)—(CH₂)_(m)—R′_(f)—COOM wherein m is 1-3, R_(f)is perfluoroalkyl or perfluoroalkoxy containing 3-8 carbon atoms, R′_(f)is linear or branched perfluoroalkylene containing 1-4 carbon atoms, andM is NH₄, Li, Na, K, or H (as described in Feiring et al., U.S. Pat. No.5,763,552).

Examples of suitable fluoroether surfactants have been described in U.S.Pat. No. 3,271,341 to Garrison; U.S. Patent Publications 2007/0015864,2007/0015865, and 2007/0015866 to Hintzer et al.; U.S. PatentPublications 2005/0090613 to Maruya et al. and 2006/0281946 to Morita etal.; PCT Patent Publications WO 2007046345 to Higuchi et al., 2007046377to Funaki et al., 2007046482 to Hoshikawa et al., and 2007/049517 toMatsuoka et al.

In accordance with a preferred embodiment of the invention, the aqueousmedium comprises less than about 300 ppm of perfluoroalkane carboxylicacid or salt fluorosurfactants having 8 or more carbon atoms, based onthe weight of water in the aqueous medium. Perfluoroalkane acid or saltfluorosurfactants having 8 or more carbon atoms include such surfactantshaving for example 8-14 carbon atoms, e.g., perfluorooctanoic acid andsalts and perfluorononanoic acid and salts. More preferably, the aqueousmedium comprises less than about 100 ppm of perfluoroalkane carboxylicacid or salt fluorosurfactants having 8 or more carbon atoms, morepreferably less than 50 ppm. In a preferred embodiment of the invention,the aqueous medium is substantially free of perfluoroalkane carboxylicacid or salt fluorosurfactants having 8 or more carbon atoms.Substantially free of perfluoroalkane carboxylic acid or saltfluorosurfactants having 8 or more carbon atoms means that aqueousmedium contains no more than about 10 ppm of such fluorosurfactants.

In a preferred embodiment the aqueous polymerization medium contains ashort chain fluorosurfactant having the formula:[R¹—O_(n)-L-A⁻]Y⁺  (I)

wherein:

-   -   R¹ is a linear or branched partially or fully fluorinated        aliphatic group which may contain ether linkages;    -   n is 0 or 1;    -   L is a linear or branched alkylene group which may be        nonfluorinated, partially fluorinated or fully fluorinated and        which may contain ether linkages;    -   A⁻ is an anionic group selected from the group consisting of        carboxylate, sulfonate, sulfonamide anion, and phosphonate; and    -   Y⁺ is hydrogen, ammonium or alkali metal cation;    -   with the proviso that the chain length of R¹—O_(n)-L- is not        greater than 6 atoms.

“Chain length” as used in this application refers to the number of atomsin the longest linear chain in the hydrophobic tail of thefluorosurfactant employed in the process of this invention. Chain lengthincludes atoms such as oxygen atoms in addition to carbon in the chainof the hydrophobic tail of the surfactant but does not include branchesoff of the longest linear chain or include atoms of the anionic group,e.g., does not include the carbon in carboxylate. “Short chain” as usedin this application refers to a chain length of not greater than 6.“Long chain” refers to a chain length of greater than 6, e.g.,fluorosurfactants having a chain length of 7 to 14 atoms.

Preferably, the chain length of R¹—O_(n)-L- is 3 to 6 atoms. Inaccordance with one preferred form of the invention the chain length ofR¹—O_(n)-L- is 4 to 6 atoms. In accordance with another preferred formof the invention the chain length of R¹—O_(n)-L- is 3 to 5 atoms. Mostpreferably, the chain length of R¹—O_(n)-L- is 4 to 5 atoms.

A preferred class of fluorosurfactants is short chain fluoroether acidsor salts, i.e., wherein n is 1 in Formula (I) above. Preferredfluoroether acids or salts in accordance with the invention arefluorosurfactants according to Formula (I) wherein:

R¹ is a linear or branched partially or fully fluorinated alkyl grouphaving 1 to 3 carbon atoms which may contain ether linkages; and

L is an alkylene group selected from —CX(R²)—, wherein R² is fluorine orperfluoromethyl and X is hydrogen or fluorine, and —CZ¹Z²CZ³Z⁴—, whereinZ¹, Z², Z³, and Z⁴ are independently selected from hydrogen or fluorine.

Fluoroether acids and salts of this type are known. When L is analkylene group selected from —CX(R²)—, wherein R² is fluorine orperfluoromethyl and X is hydrogen or fluorine, the compound can be made,for example, by hydrolysis of perfluoro-2-alkoxypropionyl fluorideintermediates prepared by reacting alkanoic acid fluorides withhexafluoropropylene oxide as disclosed in U.S. Pat. No. 3,291,843 toFritz and Selman for use in perfluoro(alkyl vinyl ether) manufacture.When L is —CZ₂CZ₂—, wherein Z is independently selected from hydrogen orfluorine, routes to making such compounds are generally described InU.S. Pat. No. 2,713,593 (Brice et al.) where fluoro(alkoxypropionic)acids and derivatives are obtained in useful yields from correspondinghydrocarbon alkoxypropionic acids and derivatives by electrochemicalfluorination. Fully fluorinated and partially fluorinated products canbe separated for example by fractional distillation. Useful teachingsfor synthesis can also be found in EP 0 148 482 B1 (Ohsaka et al.) forpartially fluorinated propoxy propionic acid fluoride which may befurther fluorinated or perfluorinated by electrofluorinating the acidfluoride which is then easily converted to an acid or salt.

In accordance with another preferred form of the invention, L in Formula(I) is an alkylene group selected from —CF(CF₃)—, —CF₂—, —CF₂CF₂—,—CHFCF₂—, and —CF₂CHF—.

The fluorosurfactant used in accordance with the invention may be adiether if R1 or L contains ether linkages. Such compounds are made, forexample, by the teachings in WO 01/46116 A1 (Hintzer et al.). Preferredfluoroether acids or salts are fluoromonoethers where R¹ and L do notcontain ether linkages.

In accordance with another preferred form of the invention, R¹ inFormula (I) is a linear partially or fully fluorinated alkyl grouphaving 2 to 3 carbon atoms. Preferably, R¹ is fully fluorinated.

In accordance with another preferred form of the invention, thefluorosurfactant is highly fluorinated. “Highly fluorinated” inreference to fluorosurfactant means that at least about 50% of the totalnumber of univalent atoms bonded to carbon in the fluorosurfactant arefluorine atoms. More preferably, at least about 75% of the total numberof univalent atoms bonded to carbon atoms in the fluorosurfactant arefluorine atoms, most preferably at least about 90%. Perfluorinatedsurfactants are also preferred for use in accordance with the invention.

In accordance with one preferred embodiment of the invention, thefluorosurfactant is a compound of the formula:[CF₃CF₂CF₂OCF(CF₃)COO⁻]Y⁺  (II)wherein Y⁺ is hydrogen, ammonium, or alkali metal cation. This compoundis represented by Formula (I) wherein R¹ is CF₃CF₂CF₂—; L is —CF(CF₃)—;A⁻ is carboxylate; and Y⁺ is hydrogen, ammonium or alkali metal cation.Preferably, Y⁺ is hydrogen or ammonium. A compound of this formula canbe obtained from the perfluoro-2-propoxypropionyl fluoride intermediateprepared according to U.S. Pat. No. 3,291,843 or by dimerization ofhexafluoropropylene oxide and subsequent hydrolysis of the resultingacid fluoride to carboxylic acid in the case of the acid and, in thecase of the salt, by simultaneous or subsequent reaction with theappropriate base to produce the desired salt. A procedure fordimerization of hexafluoropropylene oxide is disclosed in G.B. Patent1,292,268.

In accordance with another preferred embodiment of the invention, thefluorosurfactant is a compound of the formula:[CF₃CF₂OCF(CF₃)COO⁻]Y⁺  (III)wherein Y⁺ is hydrogen, ammonium, or alkali metal cation. A compound ofthis formula can be obtained from the perfluoro-2-ethoxypropionylfluoride intermediate prepared according to U.S. Pat. No. 3,291,843 andsubsequent hydrolysis of the resulting acid fluoride to carboxylic acidin the case of the acid and, in the case of the salt, by simultaneous orsubsequent reaction with the appropriate base to produce the desiredsalt.

In accordance with other embodiments of the invention, thefluorosurfactant is a compound of the formula:[C₂F₅OCF₂CF₂CF₂COO⁻]Y⁺  (IV)[C₃F₇OCF₂COO⁻]Y⁺  (V)[C₃F₇OCF₂CF₂COO⁻]Y⁺  (VI)[C₃F₇OCF₂CF₂CF₂COO⁻]Y⁺  (VII)wherein Y⁺ is hydrogen, ammonium, or alkali metal cation. Thesecompounds can be made, for example, by the procedures described in U.S.Patent Publication 2007/0015864 (Hintzer et al.).

In accordance with another embodiment of the invention, thefluorosurfactant is a compound of Formula (I) wherein n is 0; R¹ and Lcollectively comprises a perfluoroalkyl group having 4-6 carbons; and A⁻is sulfonate and sulfonamide anion. In a preferred embodiment of thisform of the invention, A⁻ is sulfonamide anion, the sulfonamide compoundof Formula (VIII) below:[C₄F₉SO₂N⁻CH₂CH₂OH]Y⁺  (VIII)wherein Y⁺ is hydrogen, ammonium, or alkali metal cation. A surfactantof this formula as the ammonium salt is available commercially from 3Munder the trademark NOVEC™ 4200.

In accordance with another embodiment of the invention, thefluorosurfactant is a compound of the formula:[CF₃CF₂CF₂CF₂CH₂CH₂SO₃ ⁻]Y⁺  (IX)wherein Y⁺ is hydrogen, ammonium, or alkali metal cation.

The surfactant can be added to the aqueous polymerization medium priorto, simultaneously with and/or subsequently to the addition of thedispersion of fluorinated ionomer particulate. In a preferredembodiment, the surfactant is supplied in salt form. If the surfactantis supplied as the corresponding acid, conversion to salt can beaccomplished by adding ammonium hydroxide or alkali metal hydroxide,preferably ammonium hydroxide, to a solution of the acid in a quantitysufficient to substantially completely convert the acid to salt formprior to adding the surfactant to the aqueous polymerization medium.Alternatively the surfactant supplied in acid form can be added to theaqueous polymerization medium and subsequently converted to salt form.

Initiators

Polymerization in accordance with the invention employs free radicalinitiators capable of generating radicals under the conditions ofpolymerization. As is well known in the art, initiators for use inaccordance with the invention are selected based on the type offluoropolymer and the desired properties to be obtained, e.g., end grouptype, molecular weight, etc. For some fluoropolymers such asmelt-processible TFE copolymers, water-soluble salts of inorganicperacids are employed which produce anionic end groups in the polymer.Preferred initiators of this type have a relatively long half-life atthe temperature of polymerization, preferably persulfate salts, e.g.,ammonium persulfate or potassium persulfate. To shorten the half-life ofpersulfate initiators, reducing agents such as ammonium bisulfite orsodium metabisulfite, with or without metal catalyst salts such as iron,can be used. Preferred persulfate initiators are substantially free ofmetal ions and most preferably are ammonium salts.

For the production of PTFE or modified PTFE dispersions for dispersionend uses, small amounts of short chain dicarboxylic acids such assuccinic acid or initiators that produce succinic acid such asdisuccinic acid peroxide (DSP) are preferably also added in addition tothe relatively long half-life initiators such as persulfate salts. Suchshort chain dicarboxylic acids are typically beneficial in reducingundispersed polymer (coagulum). For the production of PTFE dispersionfor the manufacture of fine powder, a redox initiator system such aspotassium permanganate/oxalic acid is often used.

The initiator is added to the aqueous polymerization medium in an amountsufficient to initiate and maintain the polymerization reaction at adesired reaction rate. At least a portion of the initiator is preferablyadded at the beginning of the polymerization. A variety of modes ofaddition may be used including continuously throughout thepolymerization, or in doses or intervals at predetermined times duringthe polymerization. A particularly preferred mode of operation is forinitiator to be precharged to the reactor and additional initiator to becontinuously fed into the reactor as the polymerization proceeds.Preferably, total amounts of ammonium persulfate and/or potassiumpersulfate employed during the course of polymerization are about 25 ppmto about 250 ppm based on the weight of the aqueous medium. Other typesof initiators, for example, potassium permanganate/oxalic acidinitiators, can be employed in amounts and in accordance with proceduresas known in the art.

Chain Transfer Agents

Chain-transfer agents may be used in a process in accordance with theinvention for the polymerization of some types of polymers, e.g., formelt-processible TFE copolymers, to decrease molecular weight for thepurposes of controlling melt viscosity. Chain transfer agents useful forthis purpose are well-known for use in the polymerization of fluorinatedmonomers. Preferred chain transfer agents include hydrogen, aliphatichydrocarbons, halocarbons, hydrohalocarbons or alcohol having 1 to 20carbon atoms, more preferably 1 to 8 carbon atoms. Representativepreferred examples of such chain transfer agents are alkanes such asethane, chloroform, 1,4-diiodoperfluorobutane and methanol.

The amount of a chain transfer agent and the mode of addition depend onthe activity of the particular chain transfer agent and on the desiredmolecular weight of the polymer product. A variety of modes of additionmay be used including a single addition before the start ofpolymerization, continuously throughout the polymerization, or in dosesor intervals at predetermined times during the polymerization. Theamount of chain train transfer agent supplied to the polymerizationreactor is preferably about 0.005 to about 5 wt %, more preferably fromabout 0.01 to about 2 wt % based upon the weight of the resultingfluoropolymer.

Process

In the practice of a preferred embodiment of the invention, the processis carried out as a batch process in a pressured reactor. Suitablevertical or horizontal reactors for carrying out the process of theinvention are equipped with stirrers for the aqueous medium to providesufficient contact of gas phase monomers such as TFE for desirablereaction rates and uniform incorporation of comonomers if employed. Thereactor preferably includes a cooling jacket surrounding the reactor sothat the reaction temperature may be conveniently controlled bycirculation of a controlled temperature heat exchange medium.

In a typical process, the reactor is first charged with deionized anddeaerated water of the polymerization medium and the fluorinated ionomerparticulate is dispersed in the medium. For PTFE homopolymer andmodified PTFE, paraffin wax as stabilizer is often added. A suitableprocedure for PTFE homopolymer and modified PTFE includes firstpressurizing the reactor with TFE. If used, the comonomer such as HFP orperfluoro(alkyl vinyl ether) is then added. A free-radical initiatorsolution such as ammonium persulfate solution is then added. For PTFEhomopolymer and modified PTFE, a second initiator which is a source ofsuccinic acid such as disuccinyl peroxide may be present in theinitiator solution to reduce coagulum. Alternatively, a redox initiatorsystem such as potassium permanganate/oxalic acid is used. Thetemperature is increased and, once polymerization begins, additional TFEis added to maintain the pressure. The beginning of polymerization isreferred to as kickoff and is defined as the point at which gaseousmonomer feed pressure is observed to drop substantially, for example,about 5-10 psi (about 35-70 kPa). Comonomer and/or chain transfer agentcan also be added as the polymerization proceeds. For somepolymerizations, additional monomers, surfactant, and/or initiator maybe added during the polymerization.

Batch dispersion polymerizations can be described as proceeding in twophases. The initial period of the reaction can be said to be anucleation phase during which a given number of particles areestablished. Subsequently, it can be said that a growth phase occurs inwhich the predominant action is polymerization of monomer on establishedparticles with little or no formation of new particles. The transitionfrom the nucleation to the growth phase of polymerization occurssmoothly, typically between about 4 and about 10 percent solids in thepolymerization of TFE.

The use of fluorinated ionomer in accordance with the inventiongenerally provides sufficient nucleation for the polymerization processand additional nucleating agents are not required. It is not necessaryfor stabilizing surfactants, if used, to provide additional nucleationalthough surfactants capable of effective nucleation may be used ifdesired. In accordance with one embodiment of the present invention, thenumber of dispersed fluorinated ionomer particles in the particulateintroduced into the polymerization medium is preferably selected tocontrol the number of particles formed during the nucleation phase.Preferably, the fluorinated ionomer particulate in the aqueouspolymerization medium provides a number of dispersed fluorinated ionomerparticles within about 15% of the number of fluoropolymer particlesproduced by polymerizing the fluorinated monomer. More preferably, thenumber of dispersed fluorinated ionomer particles is within about 10% ofthe number of fluoropolymer particles produced by polymerizing, morepreferably, the number of dispersed fluorinated ionomer particles iswithin about 5% of the number of fluoropolymer particles produced bypolymerizing. Most preferably, the number of dispersed fluorinatedionomer particles is approximately equal to the number of fluoropolymerparticles produced by polymerizing. The amount of fluoropolymerparticulate to be employed in a process in accordance with the inventionmay be determined by estimating the number of fluoropolymer particles tobe produced in the process based on particle size and solids content andemploying an amount of fluorinated ionomer particulate which providesapproximately the same number of particles. If other nucleating agentsare also employed in the polymerization, it may be desirable to employ asmaller number of particles of fluorinated ionomer particulate. Typicalconcentrations of dispersed fluorinated ionomer particulate are about1×10¹⁶ particles per liter to about 1×10²⁰ particles per liter.

Preferably, the amount of fluorinated ionomer particulate provided inthe aqueous polymerization medium comprises less than about 15 weight %of the fluoropolymer solids to be produced in the process. In morepreferred embodiments the amount of fluorinated ionomer particulateprovided in the aqueous polymerization medium comprises less than about10 wt %, and even more preferably less than about 1 wt %, still morepreferably about 0.1 wt % of the fluoropolymer solids to be produced inthe process and most preferably less than 0.025 wt % of thefluoropolymer solids.

If used, the amount of surfactant employed is dependent upon the desiredsolids content for the polymerization, the type of surfactant, the typeof fluoropolymer being produced, reactor design, etc. The amountsemployed can be similar to the amounts employed in conventionalpolymerizations which do not employ fluorinated ionomer particulate.Typical amounts are about 0.01 wt % to about 1 wt % based on the weightof water in the polymerization medium. When a surfactant is used whichis capable of effective nucleation, the amount employed typically willbe less than the amount employed in a conventional polymerizationwithout the use of fluorinated ionomer particulate.

The solids content of the dispersion upon completion of polymerizationcan be varied depending upon the intended use for the dispersion. Thesolids content of fluoropolymer dispersion produced by the process ofthe invention is preferably at least about 10 wt %. More preferably, thefluoropolymer solids content is at least about 20 wt %. A preferredrange for fluoropolymer solids content produced by the process is about20 wt % to about 65 wt %, even more preferably about 20 wt % to about 55wt %, most preferably, about 35 wt % to about 55 wt %.

After batch completion (typically several hours) when the desired amountof polymer or solids content has been achieved, the feeds are stopped,the reactor is vented and purged with nitrogen, and the raw dispersionin the vessel is transferred to a cooling vessel.

In a preferred process of the invention, polymerizing produces less thanabout 13 wt %, more preferably less than about 10 wt %, still morepreferably less than 3 wt %, even more preferably less than 1 wt %, mostpreferably less that about 0.5 wt % of undispersed fluoropolymer(coagulum) based on the total weight of fluoropolymer produced.

In one embodiment of the invention, the aqueous dispersion offluoropolymer particles has a raw dispersion particle size (RDPS) offrom about 10 to about 400 nm, preferably 100 to 350 nm.

The as-polymerized dispersion can be stabilized with anionic, cationic,or nonionic surfactant for certain uses. Typically, however, theas-polymerized dispersion is transferred to a dispersion concentrationoperation which produces concentrated dispersions stabilized withnonionic surfactants by known methods. Aromatic alcohol ethoxylates astaught in Marks et al., U.S. Pat. No. 3,037,953, and in Holmes, U.S.Pat. No. 3,704,272 can be used as stabilizers. Aliphatic alcoholethoxylates such as those disclosed in Marks et al., U.S. Pat. No.3,037,953 and Miura et al., U.S. Pat. No. 6,153,688 are preferably usedin concentrated dispersions stabilized with nonionic surfactants.Particularly preferred nonionic surfactants are a compound or mixture ofcompounds of the formula:R(OCH₂CH₂)_(n)OHwherein R is a branched alkyl, branched alkenyl, cycloalkyl, orcycloalkenyl hydrocarbon group having 8-18 carbon atoms and n is anaverage value of 5 to 18 as disclosed in Cavanaugh EP 1472307 A1. Thestabilized dispersion preferably contains 2-11 wt % nonionic surfactantbased on the weight of fluoropolymer solids in the dispersion. Solidscontent of concentrated dispersion is typically about 35 to about 70 wt%.

Certain grades of PTFE dispersion are made for the production of finepowder. For this use, the as-polymerized dispersion is not stabilized orconcentrated and instead is coagulated, the aqueous medium is removedand the PTFE is dried to produce fine powder.

The dispersion polymerization of melt-processible copolymers is similarto PTFE and modified PTFE polymerizations except that comonomer insignificant quantity is added to the batch initially and/or introducedduring polymerization. Chain transfer agents are typically used insignificant amounts to decrease molecular weight, i.e., to increase meltflow rate. The same dispersion concentration operation can be used toproduce stabilized concentrated dispersions. Alternatively, formelt-processible fluoropolymers used as molding resin, the dispersion iscoagulated and the aqueous medium is removed. The fluoropolymer is driedthen processed into a convenient form such as flake, chip or pellet foruse in subsequent melt-processing operations.

The process of the invention may also be carried out as a continuousprocess in a pressurized reactor. A continuous process is especiallyuseful for the manufacture of fluorocarbon elastomers.

In order to improve reaction rate and yield of such a continuouspolymerization process, the fluorinated ionomer particulate employed mayoptionally first be modified in a batch or semi-batch process wherein asmall amount of fluoromonomer(s) (i.e. preferably less than 10% of thetotal quantity of said monomers to be polymerized in the subsequentcontinuous polymerization, more preferably less than 1%, most preferablyless than 0.1%) are polymerized onto the ionomer particulate. Thismodified particulate is then introduced into the continuouspolymerization process for manufacture of fluoropolymer at improvedrates and yields.

Polymerization Products

The invention provides particles comprising a bulk of fluoropolymer anda nucleus of fluorinated ionomer. As used in this application, the term“nucleus” means an interior portion of the particle about whichfluoropolymer growth takes place as the particle is formed. Suchparticles are preferably provided as an aqueous dispersion wherein theparticles have a number average particle size of about 10 nm to about400 nm. It is preferred for the particles to comprise less than about 15wt % fluorinated ionomer. In more preferred embodiments, the particlescomprise less than about 10 wt %, and even more preferably less thanabout 1 wt %, still more preferably about 0.1 wt %, and most preferablyless than 0.025 wt % of fluorinated ionomer.

In preferred forms of the invention, the fluoropolymer of the particlesis a homopolymer or copolymer of at least one fluorinated monomerselected from the group consisting of tetrafluoroethylene (TFE),hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE),trifluoroethylene, hexafluoroisobutylene, perfluoroalkyl ethylenes,fluorovinyl ethers, vinyl fluoride (VF), vinylidene fluoride (VF2),perfluoro-2,2-dimethyl-1,3-dioxole (PDD),perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD), perfluoro(allylvinyl ether) and perfluoro(butenyl vinyl ether). In one embodiment, thefluoropolymer comprises polytetrafluoroethylene or modifiedpolytetrafluoroethylene having a comonomer content of no greater thanabout 1 wt %. In another embodiment, the fluoropolymer comprisesmelt-processible copolymer comprising at least about 60-98 wt %tetrafluoroethylene units and about 2-40 wt % of at least one othermonomer. In yet another embodiment, the fluoropolymer comprisesfluorocarbon elastomer. Preferred fluorocarbon elastomer comprisescopolymers comprising 25 to 70 wt %, based on total weight of thefluorocarbon elastomer, of copolymerized units of a first fluorinatedmonomer selected from the group consisting of vinylidene fluoride (VF2),tetrafluoroethylene (TFE), and mixtures thereof.

Particles in accordance with the invention comprising a bulk offluoropolymer and a nucleus of fluorinated ionomer and dispersionsthereof can be employed generally in the same manner as conventionalfluoropolymer particles and dispersions.

In accordance with one form of the invention, articles are formed fromthe particles of the invention. When in the form of fine powder, thefluoropolymer is commonly converted to useful articles by a lubricatedextrusion (paste extrusion) process. In paste extrusion, the resin isblended with a lubricant and shaped by an extrusion process. Afterextrusion, the lubricant is removed, and the resultant green shape isfused (sintered) at temperature above the melting point of the PTFE.Articles formed from fine powder resin include paste extruded tubing,wire and cable coatings and sheet or tape. Another article is expandedPFTE films which are made from paste extruded shapes that are rapidlystretched in the unsintered state to form film that is porous to watervapor but not to condensed water, and is useful in material forgarments, tenting, separatory membranes, and the like.

In accordance with another form of the invention, articles are formedfrom melt processable fluoropolymers such as PFA and FEP. Such articlesare commonly fabricated by melt extrusion to create coverings for wireand cable, tubing and pipe. Film can be formed by casting the extrudedmolten film onto a chilled roller. Thin film can be formed by the filmblowing technique. In making blown film, molten polymer is continuouslyextruded upward from a circular die to form a film tube. The film tubeis rapidly expanded by internal pressure while the film is still moltenand then, at a height above the die where the polymer has cooled andsolidified, is nipped or slit and wound up. Small parts can befabricated by injection molding; these parts can include shapes ofconsiderable complexity that do not require further shaping bymachining. Larger shapes can be fabricated by the transfer moldingtechnique, in which an aliquot of resin from a reservoir or “pot” ofmolten polymer is injected by a plunger into a preheated mold.

In accordance with another form of the invention, coatings are formedfrom the particles of the invention whether applied as powders ordispersed in water or organic solvents or a mixture thereof.

In yet another form of the invention, an article is provided having acoating formed from an aqueous dispersion of the particles of theinvention. Coated articles include cookers and fry pans, oven liners,glass fabric and the like. Other coated articles include valves, wire,metal foil, shoe molds, snow shovels and plows, ship bottoms, chutes,conveyors, dies, tools, industrial containers, molds, lined reactorvessels, automotive panels, heat exchangers, tubing, and the like.Coated articles also include o-rings, gaskets, seals, beading,windshield wipers, and automotive window and door seals, rubber rollsfor photocopiers and laser printers including fuser and pressure rolls,rubber belts for photocopiers, and the like. Coated articles furtherinclude shower doors, oven and microwave glass, lenses, head lamps,mirrors, automobile windshields, cathode ray tubes such as used intelevision sets and computer monitors, laboratory glassware, and vialsfor pharmaceuticals. Additionally, coated articles include flat paneldisplays such as liquid crystal displays and light emitting diodes,photoconductor rolls for photocopiers and laser printers, electronicdevices wherein coatings are interlayer dielectrics, photomasks, and thelike. Moreover, coated articles include statuary, architectural panelsand buildings, and the like.

Test Methods

Melt Flow Rate (MFR) of the Fluorinated Ionomer is measured on thepolymer in thermoplastic form, e.g., the sulfonyl fluoride or sulfonicacid form for sulfonate ionomers, according to the method of ASTMD-1238-04c at 270° C. with a 2110 gram weight.

Fluorinated Ionomer Particulate Size, Weight Average, is measured bydynamic light scattering (DLS). Dispersions of the ionomers were dilutedfrom 10× to 100× (vol:vol), but typically 30×, into a dispersant ofdimethyl sulfoxide with additives of 0.1 wt % (solids basis) of Zonyl®1033D (C₆F₁₃CH₂CH₂SO₃H) surfactant and 0.23 wt % ethyldiisopropylamine,which neutralized the Zonyl® and the ionomer end groups totrialklyammonium forms. This dispersant mixture was called “DMSOZE”. Thediluted dispersion was filtered through a 1.0 um graded density glassmicro fiber syringe filter (Whatman PURADISC® #6783-2510) into adisposable polystyrene cuvette. Dynamic light scattering (DLS) wasmeasured at 25° C. using a Malvern Instruments Nano S, which measuresscattered light from a HeNe laser at 633 nm at a scattered angle of 173°(close to backscattered). The automated instrument chooses how many 10 sruns make up each measurement (generally 12 to 16), and for each sampleten measurements were performed, the entire process taking usually ˜30min. For concentrated or highly scattering samples, the instrument maymove the focal point of the laser close to the front of the cuvette,minimizing the path length through the sample and thus reducingparticle-particle scattering artifacts. However, for almost all thefluorinated ionomer dispersion samples analyzed here, the instrumentchose to use a focal position of 4.65 mm, which maximized the path inthe cell and enhanced detection of the weak scattering. In addition, theinstrument adjusts an attenuator to maintain the count rate in anoptimum range. The attenuator settings were 11, 10, or 9, whichcorrespond to light attenuation factors of X1.00 (no attenuation),X0.291, or X0.115, respectively. Various numeric and graphical outputsare available from the Malvern software. The simplest and most robust isthe “z-average” particle diameter, calculated from the z-averagediffusion coefficient made by a cumulants fit to the autocorrelationfunction. The name z-average has been used in analogy to the z-averagemolecular weight Mz, in that the DLS z-average particle size is derivedfrom a distribution of diffusion coefficients weighted by the square ofthe particle mass M_(i) ². Half of the scattered light Intensity isproduced by particles with diameters larger than D(I)50. Using the inputrefractive index of the particles, dispersant index, wavelength, andscattering angle, the software uses a Mie calculation to convert theintensity distribution to a weight distribution. The weight averagediameter is that diameter at which half of the mass of the particles inthe sample have a larger diameter and half have a smaller diameter.

Dry coaqulum amount is measured by physically collecting the wet polymerthat coagulates during the course of the polymerization and then dryingthis coagulum overnight at 80° C. and a vacuum of 30 mm Hg (4 kPa). Thedried coagulum is weighed and the Weight Percentage of UndispersedPolymer (Coaq. wt %) is determined based on the total weight offluoropolymer in the dispersion.

Transition Temperatures of Fluoropolymers by Differential ScanningCalorimetry (DSC) is measured according to ASTM D 3418-03.

Melt Flow Rate (MFR) of the Fluoropolymer Produced in the Process ismeasured according to ASTM D-1238-94a following the detailed conditionsdisclosed in U.S. Pat. No. 4,952,630 at 372° C.

Comonomer content (PPVE) is measured by FTIR according to the methoddisclosed in U.S. Pat. No. 4,743,658, col. 5, lines 9-23.

Weight % Fluorinated Ionomer in Fluoropolymer Dispersion Particles (FINucleus) is calculated by dividing the weight of dispersed fluorinatedionomer particulate charged to the reactor by the total weight offluoropolymer in the dispersion.

Fluoropolymer Particle size, i.e., raw dispersion particle size (RDPS)is determined by laser diffraction techniques that measure the particlesize distributions (PSD) of materials using a Microtrac UltrafineParticle Analyzer (UPA). The UPA uses dynamic light scattering principlefor measuring PSD with size range of 0.003 micron to 6.54 micron. Thesamples were analyzed after collecting the background with water. Themeasurements were repeated three times and averaged.

Perfluoroalkane Carboxylic Acid Or Salt Fluorosurfactant Content ismeasured by a GC technique in which the fluorosurfactant is esterifiedwith acidic methanol. Perfluoroheptanoic acid is used as an internalstandard. Upon addition of electrolyte and hexane the ester is extractedinto the upper hexane layer. The hexane layer is analyzed by injectiononto a glass GC column of 20 ft.×2 mm I.D. packed with 10% OV-210 on70/80 mech Chromosorb W.AW.DMCS. held at 120 C. The detector is ECD andthe carrier gas of 95% argon/5% methane has a flow rate of 20 to 30ml/min.

EXAMPLES

Fluorinated Ionomer Particulate

Aqueous dispersion of fluorinated ionomer particulate (FI) is preparedaccording to the procedure described as Example 4 in U.S. Pat. No.7,166,685, (fluorinated ionomer in the acid form) using TFE/PDMOFfluorinated ionomer resin having an IXR of 12.1 (EW of 950) and a meltflow in its sulfonyl fluoride form of 24. The aqueous dispersion offluorinated ionomer particulate has a solids content of 21.4 wt % withthe fluorinated ionomer particulate having a weight average diameter of5.23 nm. The ionic groups have a pKa of about 1.9 as measured on thefluorinated ionomer in aqueous dispersion form having 10 wt % solids atroom temperature.

Surfactants

Except as indicated, surfactants are employed in the form of aqueoussolutions made using deionized water to provide percentages of salt inthe solutions indicated below:

-   Surfactant 1 (S1): CF₃(CF₂)₆COONH₄ (ammonium perfluorooctanoate,    APFO), 20 wt %-   Surfactant 2 (S2): C₃F₇OCF(CF₃)COONH₄ (HFPO dimer acid salt, DAS),    86.4 wt % (Prepared by dropwise addition of 128 g of concentrated    ammonium hydroxide solution to 500 g of C₃F₇OCF(CF₃)COOH without    subsequent dilution.)-   Surfactant 3 (S3): C₃F₇O(CF₂)₂COONH₄, 20 wt %-   Surfactant 4 (S4): C₃F₇O(CF₂)₃COONH₄, 20 wt %-   Surfactant 5 (S5): C₂F₅O(CF₂)₃COONH₄, 20 wt %-   Surfactant 6 (S6): C₂F₅O(CF₂)₂OCF₂COONH₄, 20 wt %-   Surfactant 7 (S7): C₃F₇(CH₂)₄COONH₄, 20 wt %-   Surfactant 8 (S8): CF₃(CF₂)₄COONH₄, 20 wt %-   Surfactant 9 (S9): CF₃(CF₂)₃COONH₄, 20 wt %-   Surfactant 10 (S10): C₃F₇OCF₂COONH₄, 20 wt %-   Surfactant 11 (S11): Sodium Octylsulfonate (SOS), 44 wt %-   Surfactant 12 (S12): C₃F₇OCF(CF₃)—CH₂—O—PO(OH)O⁻NH₄ ⁺ (HFPO dimer    phosphate ester, made according to the process disclosed in WO    2009094344 A1), 20 wt %

Comparative Example 1

A conventional process is illustrated in the polymerization ofcopolymers of tetrafluoroethylene (TFE) with perfluoro(alkyl vinylether), i.e., perfluoro(propyl vinyl ether) (PPVE) using Surfactant1—APFO as the surfactant in a 1.8 liter reactor.

Surfactant Solution (S1): 20 wt % APFO in deionized water

Initiator Solution: 1.00 g ammonium persulfate (from Sigma-AldrichCorporation St. Louis, Mo., USA) in 1000 g deionized water (0.1%ammonium persulfate solution).

Deaerated water is used in the polymerization. It is prepared bydispensing deionized water into a 1 gallon plastic vessel and vigorouslybubbling nitrogen gas through the water to remove oxygen. The deareatedwater is removed as needed from this plastic vessel for use in thepolymerization.

The reactor is a 1.8 liter (total volume), vertical autoclave made ofHastelloy®. A 45° pitch, downward, propeller-type agitator and a singleblade baffle is used for agitation. The bottom of the reactor has a ¼″port, through which liquid samples may be taken during the course of thereaction. No chain transfer agent is used.

The reactor is charged with a solution of 800 g deaerated water and 6.43g APFO surfactant solution, by pouring the precharge materials throughan open port on the top of the reactor. The surfactant solution is addeddirectly to the reactor in the deaerated water to avoid anycross-contamination that might arise in piping surfactants into thereactor. The deaerated water and APFO solution make up the reactorprecharge.

After precharging the solution to the reactor, the computer program,which controls the operations of the reactor, is started and the vesselis agitated at 100 RPM. At the beginning of the polymerization,agitation is increased to 870 rpm and the reactor is purged three timesby pressurization with nitrogen gas to 250 PSIG (1723 kPa) followed byventing to 1 PSIG (7 kPa) to reduce oxygen content. While continuing toagitate the reactor at 870 rpm, the system is purged three more times bypressurization with gaseous tetrafluoroethylene (TFE) to 40 PSIG (274kPa) followed by venting to 1 PSIG (7 kPa), further insuring that thecontents of the autoclave are free of oxygen. The reactor is then heatedto 75° C. Perfluoro(propyl vinyl ether) (PPVE) (13.6 ml) is pumped as aliquid into the reactor for one minute at the constant rate of 13.6ml/min, via a 100 ml capacity syringe pump sold by Teledyne Isco.

The temperature within the reactor is maintained throughout thepolymerization at 75° C. When the precharge of PPVE has been fed and thereactor temperature is stabilized at 75° C., the reactor pressure israised to 350 PSIG (2.4 MPa), by adding TFE through a pressure regulatorinto the reactor. When the reactor reaches 350 PSIG, the TFE supply tothe reactor is valved off. Pumping of the initiator solution (APS) intothe reactor is simultaneously initiated at a rate of 80 ml/min for 24seconds followed by a rate of 0.4 ml/min. until the end of the batch.

At kickoff (the point at which a 10 PSIG (69 kPa) pressure drop isobserved) the polymerization is deemed to have been started, which isalso the start point for feeding PPVE at a rate of 0.128 ml/min. for therest of the polymerization. Reactor pressure is kept constant at 350PSIG (2.4 MPa) by feeding TFE as needed throughout the entirepolymerization. The sampling mechanism on the reactor allows for fourliquid samples of about 10 ml/each to be taken during the course of thereaction.

The batch end is defined as the point at which 144 g of TFE has been fedto the reactor through a mass flow controller. After 144 g of TFE isconsumed, all feeds to the reactor are shut off, and the contents arecooled to 30° C. over the course of about 15 minutes. The agitation isreduced to 100 rpm and the reactor is then vented to atmosphericpressure and purged 3 times with N₂ to 150 PSIG.

The fluoropolymer dispersion produced has a solids content of 15.34 wt%.

Polymer is isolated from the dispersion by freezing, thawing andfiltration. The polymer is washed with deionized water and filteredseveral times before being dried overnight in a vacuum oven at 80° C.and a vacuum of 30 mm Hg (4 kPa). Reaction conditions and polymerproperties are reported in Tables 1a and 1b.

Example 1 TFE/PPVE Polymerization Using Dispersed Fluorinated IonomerParticulate

This example demonstrates the polymerization of TFE/PPVE copolymer inthe presence of dispersed particulate of fluorinated ionomer in a 1.8liter reactor.

The general procedure of Comparative Example 1 is followed except that asolution of APFO is not employed. Instead, a solution made from 800 gdeareated water and 2.00 g of the 21.4 wt % aqueous dispersion offluorinated ionomer particulate described above is added to the reactoras the precharge. PPVE, TFE and APS were added as in Comparative Example1 until 140 g of TFE had been consumed. Reaction conditions and polymerproperties are reported in Tables 1a and 1b.

TABLE 1a TFE/PPVE Polymerization Using Dispersed Fluorinated IonomerParticulate Amount Surfactant Amount Run Surfactant or FI Solution TFEKickoff Time Example or FI g g min min Comp Ex 1 APFO (S1) 6.42 144 8 90Ex 1 Fluorinated 2.00 140 7.5 200 Ionomer

TABLE 1b TFE/PPVE Polymerization Using Dispersed Fluorinated IonomerParticulate Surfactant RDPS Solids FI Nucleus Dry Coag Coag DSC PPVE Ex.No. or FI nm % wt % g wt % (° C.) wt % Comp Ex 1 APFO (S1) 105 15.3 0.007.2 8.0 322.74 6 Ex 1 Fluorinated 98 17.9 0.32 0.3 0.2 321.26 14.8Ionomer

Comparative Example 2

A conventional process is illustrated in the polymerization ofcopolymers of tetrafluoroethylene (TFE) with perfluoro(alkyl vinylether), i.e., perfluoro(propyl vinyl ether) (PPVE) using Surfactant1—APFO as the surfactant in a 1 gallon horizontal autoclave.

Surfactant Solution (S1): 20 wt % APFO in deionized water

Initiator Solution: 1.5 g ammonium persulfate (from Sigma-AldrichCorporation St. Louis, Mo., USA) in 1498.5 g deionized water (0.1%ammonium persulfate solution).

Deaerated water is used in the polymerization. It is prepared by pumpingdeionized water into a large plastic vessel and vigorously bubblingnitrogen gas through the water to remove all oxygen. The deareated wateris removed as needed from this plastic vessel for use in thepolymerization.

The reactor is a 1 gallon horizontal autoclave made of Hastelloy®,equipped with an extended anchor-type agitator, which has a centralshaft in the middle that runs the length of the clave. The end furthestfrom the drive is closed and the outer blades sweep the inside of theclave body within an inch or two of the interior wall. No chain transferagent is used.

The reactor is charged by means of a syringe pump with 1850 g ofdeaerated water. Through an open port, 25.7 g of the 20% APFO surfactantsolution is pipetted into the reactor. The surfactant is added directlyto the reactor from the pipette to avoid any cross-contamination thatmight arise in piping surfactants into the reactor. The deaerated waterand APFO solution make up the reactor precharge.

The vessel is agitated at 100 RPM for 3-5 minutes and then the agitatoris stopped. The reactor is then purged three times (agitator off) bypressurization with nitrogen gas to 80 PSIG (650 kPa) followed byventing to 1 PSIG (108 kPa) to reduce oxygen content. It is furtherpurged three times (agitator off) by pressurization with gaseoustetrafluoroethylene (TFE) to 25 PSIG (274 kPa) followed by venting to 1PSIG (108 kPa) further insuring that the contents of the autoclave arefree of oxygen. The agitator rate is then increased to 100 RPM, thereactor is heated to 75° C., and then perfluoro(propyl vinyl ether)(PPVE) (31.5 ml) is pumped as a liquid into the reactor for one minuteat the constant rate of 31.5 ml/min.

When the vessel temperature equilibrates at 75° C., the reactor pressureis raised to a nominal 250 PSIG (1.83 MPa) by adding TFE through apressure regulator into the reactor. Initiator Solution is then pumpedto the reactor at a rate of 105.7 ml/min for 1 min. followed by a rateof 1.01 ml/min. until the end of the batch, which is defined as thepoint at which 333 g of TFE are fed to the reactor through a mass flowcontroller.

At kickoff (the point at which a 10 PSIG (70 kPa) pressure drop isobserved) the polymerization is deemed to have been started, which isalso the start point for feeding PPVE at a rate of 0.30 g/min. for therest of the polymerization. Reactor pressure is kept constant at 250PSIG (1.83 MPa) by feeding TFE as needed throughout the entirepolymerization.

After 333 g of TFE are consumed, all feeds to the reactor are shut off,and the contents are cooled to 30° C. over the course of about 90minutes. The reactor is then vented to atmospheric pressure.

The fluoropolymer dispersion thus produced has a solids content of 21.78wt %.

Polymer is isolated from the dispersion by freezing, thawing andfiltration. The polymer is washed with deionized water and filteredseveral times before being dried overnight in a vacuum oven at 80° C.and a vacuum of 30 mm Hg (4 kPa). Reaction conditions and polymerproperties are reported in Tables 2a and 2b.

Example 2 TFE/PPVE Polymerization Using Dispersed Fluorinated IonomerParticulate and Surfactant

This example demonstrates the polymerization of TFE/PPVE copolymer inthe presence of dispersed fluorinated ionomer particulate in combinationwith a variety of different fluorosurfactants in a 1 gallon horizontalautoclave.

The general procedure of Comparative Example 2 is followed except that asolution of APFO is not employed. Instead, the 21.4 wt % aqueousdispersion of fluorinated ionomer particulate described above and anaqueous solution of surfactant in the concentrations indicated above andin the amounts as indicated in Table 2a are precharged to the reactor.Reaction conditions and polymer properties are reported in Tables 2a and2b.

TABLE 2a TFE/PPVE Polymerization Using Dispersed Fluorinated IonomerParticulate and Surfactant Amount FI/Surf. Amount Est. conc. of AmountRun Solution TFE FI particles Surfactant Kickoff Time Ex. No. FI/Surf. gg #/liter mmol/kg* min min Comp 2 S1 (APFO)   0/79.6 335 0 17.5 8 83 Ex2a FI/S2 2.4/11.8 336 3.2E17 14 3 65 Ex 2b FI/S3 2.4/73.2 336 3.2E17 143 67 Ex 2c FI/S4 2.4/84.0 337 3.2E17 14 2 62 Ex 2d FI/S5 2.4/46.8 3353.2E17 9 2 65 Ex 2e FI/S6 2.4/76.8 338 3.2E17 14 3 59 Ex 2f FI/S72.4/37.2 272 3.2E17 7 6 147 Ex 2g FI/S8 2.4/34.3 343 3.2E17 7 2 61 Ex 2hFI/S9 7.2/27.6 326 9.6E17 7 8 77 Ex 2i FI/S10 7.2/30.8 329 9.6E17 7 3 68*Based on the weight of the fluoropolymer dispersion produced

TABLE 2b TFE/PPVE Polymerization Using Dispersed Fluorinated IonomerParticulate and Surfactant Est. conc. of RDPS Solids FI Nucl Dry CoagCoag DSC PPVE polymer particle Ex. No. FI/Surf. nm % wt % G % (° C.) wt% #/liter Comp 2 S1 (APFO) 93 21.78 0.000 88.7 15.2% 326.2 12.5 3.1E172a FI/S2 76 21.54 0.090 21.8 3.8% 323.1 7.1 5.6E17 2b FI/S3 93 20.620.094 21.9 4.0% 323.7 8.7 2.9E17 2c FI/S4 90 20.12 0.088 72.5 12.6%324.2 8.7 3.2E17 2d FI/S5 97 21.69 0.088 10 1.7% 322.8 6.6 2.7E17 2eFI/S6 95 21.78 0.092 23.8 4.3% 323.3 6.8 2.9E17 2f FI/S7 106 25.87 0.0736.4 0.9% 324.8 10.9 2.5E17 2g FI/S8 78 24.02 0.094 1.1 0.2% 322.6 8.35.8E17 2h FI/S9 24 22.43 0.263 4.1 0.7% 322 7.3 1.9E19 2i FI/S10 10623.58 0.289 1.6 0.3% 322.8 6.3 2.3E17

Example 3 TFE/PPVE Polymerization Using Dispersed Fluorinated IonomerParticulate and Surfactant

This example demonstrates the polymerization of TFE/PPVE copolymer inthe presence of a variety of dispersed fluorinated ionomer particulatewith differing molecular weights and equivalent weights and made usingdiffering dissolution conditions, each in combination with a short chainfluoroether surfactant (Surfactant 2—DAS), in a 1 gallon horizontalautoclave.

The general procedure of Comparative Example 2 is followed except that asolution of APFO is not employed. Instead, the various dispersions offluorinated ionomer particulate described in Table 3a are precharged tothe reactor in amounts to provide the estimated concentration offluorinate ionomer particles and the 86.4% aqueous solution ofSurfactant 2 (DAS) is precharged to the reactor to provide aconcentration of about 7 mmol/kg based on the weight to fluoropolymerdispersion produced. Dispersed fluorinated ionomer particulateproperties, reaction conditions and polymer properties are reported inTables 3a, 3b and 3c.

TABLE 3a TFE/PPVE Polymerization Using Various Dispersed FluorinatedIonomer Particulate and Surfactant 2 (DAS) FI Dissolution FI DissolutionWeight Average FI Est. Conc. of FI Equivalent FI Melt Temp Time ParticleDiameter FI Particles Ex. No. Weight/IXR Flow C. min nm #/liter Ex 3a950/12.1 n/m* 270 <5 5.23 3.2E17 Ex 3b 1000/13.1  n/m* 270 <5 5.533.2E17 Ex 3c 939/11.9   18.6 270 30 5.67 3.2E17 Ex 3d 987/12.9 24 300 55.41 3.2E17 Ex 3e 1005/13.2  16 270 5 5.84 3.2E17 Ex 3f 987/12.9 24 2705 5.31 3.2E17 Ex 3g 1446/22.0  n/m* 300 5 8.40 3.2E17 Ex 3h 993/13.0 34270 5 5.45 3.2E17 Ex 31 987/12.9 24 270 480 5.20 3.2E17 Ex 3j 1201/17.1 10 300 5 6.22 3.2E17 Ex 3k 987/12.9 24 210 5 5.91 3.2E17 Ex 3l 987/12.924 270 5 5.41 3.2E17 Ex 3m 987/12.9 24 240 5 2.55 3.2E17 *n/m = notmeasured

TABLE 3b TFE/PPVE Polymerization Using Dispersed Fluorinated IonomerParticulate and Surfactant 2 (DAS) Amount TFE Kickoff Run Time Ex. No. gmin min Ex 3a 326 3 80 Ex 3b 335 3 75 Ex 3c 366 4 66 Ex 3d 314 1 57 Ex3e 325 3 67 Ex 3f 334 2 72 Ex 3g 333 3 91 Ex 3h 323 1 63 Ex 31 325 2 56Ex 3j 327 1 74 Ex 3k 335 2 83 Ex 3l 330 2 69 Ex 3m 337 1 69

TABLE 3c TFE/PPVE Polymerization Using Dispersed Fluorinated IonomerParticulate and Surfactant 2 (DAS) Est. conc. of RDPS Solids FI NucleusDry Coag Coag DSC PPVE polymer particle Ex. No. nm % wt % g % (° C.) wt% #/liter Ex 3a 92 24.1 0.081 5.0 0.8 323.7 9.5 3.6E17 Ex 3b 88 23.80.096 11.8 1.9 322.8 7.5 4.0E17 Ex 3c 88 25.0 0.115 8.4 1.5 321.4 3.24.2E17 Ex 3d 92 21.7 0.102 4.2 0.8 322.3 5.8 3.2E17 Ex 3e 82 22.2 0.1228.0 1.4 322.3 6.2 4.6E17 Ex 3f 87 22.3 0.083 3.2 0.5 322.8 6.0 3.9E17 Ex3g 61 25.2 0.311 3.2 0.5 322.2 6.4 1.3E18 Ex 3h 85 22.9 0.098 2.9 0.5322.2 4.9 4.3E17 Ex 31 81 22.6 0.087 2.3 0.4 323.3 5.9 4.9E17 Ex 3j 7923.6 0.140 1.9 0.3 322.8 7.2 5.5E17 Ex 3k 75 24.1 0.122 2.1 0.3 323.27.9 6.6E17 Ex 3l 85 22.0 0.106 2.1 0.4 323.2 6.4 4.1E17 Ex 3m 107 22.80.010 8.9 1.5 324.0 5.9 2.1E17

Example 4 TFE/PPVE Polymerization Using Dispersed Fluorinated IonomerParticulate and Surfactant 2 (DAS)

This example demonstrates the polymerization of TFE/PPVE copolymer inthe presence of dispersed fluorinated ionomer particulate and a shortchain fluoroether surfactant (Surfactant 2—DAS) in a 1 gallon horizontalreactor.

A cylindrical, horizontal, water-jacketed, paddle-stirred, stainlesssteel reactor having a length to diameter ratio of about 3.0 and a watercapacity of 1 gallon (3.79 liter) is charged with 2000 ml of deionizedwater, 1 g of the 21.4 wt % aqueous dispersion of fluorinated ionomerparticulate described above, and 3.54 g of Surfactant 2 (DAS) (86.4% wt% solution HFPO dimer acid salt). With the reactor paddle agitated at125 rpm, the reactor is evacuated and purged three times withtetrafluoroethylene (TFE) at 25° C. Ethane is added to the reactor untilthe pressure is 8 in Hg (3.93 psig, 0.0271 MPa), then the temperature ofthe reactor is raised to 75° C. After the temperature has become steadyat 75° C., twenty milliliters of perfluoropropyl vinyl ether (PPVE) areadded, then the pressure in the reactor is raised to 300 psig (2.07 MPa)with TFE. Forty milliliters of a freshly prepared aqueous initiatorsolution containing 0.20 wt % ammonium persulfate are charged to thereactor. This same initiator solution is pumped into the reactor at 0.5ml/min for the remainder of the batch. After polymerization had begun,as indicated by a 10 psig (0.07 MPa) drop in reactor pressure,additional TFE is added to the reactor at a rate of 0.0167 lb/min (7.56g/min) until a total of 2.0 lb (907.2 g) of TFE are added after kickoff.PPVE is added at 0.2 ml/min for the duration of the batch, 120 min. Atthe end of the reaction period, the TFE, PPVE, and initiator feeds arestopped and the reaction vessel is vented. The amount of raw dispersionobtained is 3006 g. Solids content of the dispersion is 31.4 wt %, andthe raw dispersion particle size (RDPS) is 150 nm. The wt % ofundispersed polymer is 2.3%. The wt % of fluorinated ionomer in thedispersion particles (FI Nucleus) is calculated to be 0.023 wt %.

The dispersion is coagulated by freezing and subsequently thawing. Aftercoagulation, the polymer is isolated by filtering and then dried in a150° C. convection air oven. This PPVE/TFE copolymer had a melt flowrate (MFR) of 6.9 g/10 min, a PPVE content of 2.78 wt %, a melting pointof 311° C., and an MIT flex life of 4880 cycles.

Example 5 TFE/HFP/PEVE Polymerization Using Dispersed FluorinatedIonomer Particulate and Surfactant 2 (DAS)

This example demonstrates the polymerization of TFE/HFP/PEVE copolymerin the presence of dispersed fluorinated ionomer particulate and a shortchain fluoroether surfactant (Surfactant 2—DAS) in a 1 gallon horizontalreactor.

A cylindrical, horizontal, water-jacketed, paddle-stirred, stainlesssteel reactor having a length to diameter ratio of about 3.0 and a watercapacity of 1 gallon (3.79 l) is charged with 2000 ml of dimineralizedwater, 0.6 g of the 21.4 wt % aqueous dispersion of fluorinated ionomerparticulate described above, and 6.2 g of Surfactant 2 (DAS) (86.4% wt %solution HFPO dimer acid salt). With the reactor paddle agitated at 125rpm, the reactor is heated to 65° C., evacuated and purged three timeswith tetrafluoroethylene (TFE). The reactor temperature then isincreased to 103° C. After the temperature had become steady at 103° C.,hexafluoropropylene (HFP) is added slowly to the reactor until thepressure is 430 psig (2.96 MPa). After the temperature had equilibratedagain to 103° C., 9.2 milliliters of liquid PEVE is injected into thereactor. TFE is added to the reactor to achieve a final pressure of 630psig (4.34 MPa). Then 4.0 ml of freshly prepared aqueous initiatorsolution containing 4.4 wt % of ammonium persulfate (APS) is injected.This same initiator solution is pumped into the reactor at 0.4 ml/minfor the remainder of the polymerization. After polymerization had begunas indicated by a 10 psig (0.07 MPa) drop in reactor pressure,additional TFE is added to the reactor at a rate of 0.017 lb/min (7.71g/min) until a total of 2.13 lbs (966 g) of TFE had been added to thereactor after kickoff. Furthermore, liquid PEVE is added at a rate of0.1 ml/min for the duration of the reaction. The total reaction time is125 min after initiation of polymerization. At the end of the reactionperiod, the TFE feed, PEVE feed, and the initiator feed are stopped, andthe reactor is cooled while maintaining agitation. When the temperatureof the reactor contents reached 90° C., the reactor is slowly vented.After venting to nearly atmospheric pressure, the reactor is purged withnitrogen to remove residual monomer. Upon further cooling, thedispersion is discharged from the reactor at below 70° C. The amount ofraw dispersion obtained is 2892 g. Solids content of the dispersion is36.8 wt % and raw dispersion particle size (RDPS) is 177 nm. The wt % ofundispersed polymer is 7.0%. The wt % of fluorinated ionomer in thedispersion particles (FI Nucleus) is calculated to be 0.012 wt %.

The dispersion is coagulated by freezing and subsequently thawing. Aftercoagulation, the polymer is isolated by filtering and then drying in a150° C. convection air oven. This polymer is stabilized by heating at260° C. for 1.5 hr in humid air containing 13 mol % water. TheTFE/HFP/PEVE terpolymer had a melt flow rate (MFR) of 14.8 g/10 min, anHFP content of 10.15 wt %, a PEVE content of 0.77 wt %, and a meltingpoint of 250.7° C. This example demonstrates the polymerization ofTFE/HFP/PEVE in the presence of dispersed fluorinated ionomerparticulate and short chain surfactant.

Example 6 PTFE Polymerization Using Dispersed Fluorinated IonomerParticulate and Surfactant 2 (DAS)

This example demonstrates the polymerization of PTFE in the presence ofdispersed fluorinated ionomer particulate and a short chain fluoroethersurfactant (Surfactant 2—DAS).

A cylindrical, horizontal, water-jacketed, paddle-stirred, stainlesssteel reactor having a length to diameter ratio of about 3.0 and a watercapacity of 1 gallon (3.79 liter) is charged with 1800 ml ofdimineralized water, 0.13 g of the 21.4 wt % aqueous dispersion offluorinated ionomer particulate described above, and 9.3 g of Surfactant2 (DAS) (86.4% wt % solution HFPO dimer acid salt). Additionally, 90grams of paraffin wax, and 0.65 ml of a solution containing 1.42 gFeCl₂.4H₂O and 0.1 ml HCl per 100 ml water are added. With the reactorpaddle agitated at 125 rpm, the reactor is heated to 65° C., thenevacuated and purged three times with tetrafluoroethylene (TFE). Next,6.3 ml of a 1 wt % solution of methanol in water, and 0.75 ml of a 1 wt% aqueous solution of Triton® X-100 are added. The reactor temperatureis increased to 90° C. After the temperature equilibrated to 90° C., thepressure in the autoclave is raised to 370 psi (2.55 MPa) using TFE,then 40 ml of a solution composed of 6.2 wt % disuccinyl peroxide (DSP)and 0.046 wt % ammonium persulfate (APS) are added at a rate of 6ml/min. After polymerization had begun, as indicated by a 10 psig (0.07MPa) drop in reactor pressure, additional TFE is added to the reactor atto maintain the desired pressure of 370 psi (2.55 MPa), while limitingTFE consumption to no more than 0.06 lb/min (27.2 g/min) by varyingagitator speed. After 0.3 lbs (136.1 g) of TFE had reacted, additionalSurfactant 2 (DAS), 100 ml of a 6.22 wt % aqueous solution of HFPO dimeracid salt, is added at a rate of 5 ml/min. After 2.8 lbs (1270 g) of TFEhad been consumed, the reaction is terminated by stopping the TFE. Theduration of the reaction is 55 min. The contents are discharged from thepolykettle and the supernatant wax is removed. The amount of rawdispersion obtained is 3142 g. The solids content of the raw dispersionis 39.3 wt % and the raw dispersion particle size (RDPS) is 221 nm. Thewt % of undispersed polymer is 4.4%. The wt % of fluorinated ionomer inthe dispersion particles (FI Nucleus) is calculated to be 0.00225 wt %.

The dispersion is coagulated by freezing and subsequently thawing. Aftercoagulation, the polymer is isolated by filtering and then drying in a150° C. convection air oven. The PTFE resin had a standard specificgravity (SSG) of 2.237.

Example 7 Perfluoroelastomer Polymerization Using Dispersed FluorinatedIonomer Particulate and Surfactant 2 (DAS)

This example demonstrates the polymerization of a perfluoroelastomer inthe presence of dispersed fluorinated ionomer particulate and shortchain fluoroether surfactant (Surfactant 2—DAS).

A perfluoroelastomer containing copolymerized monomers oftetrafluoroethylene (TFE), perfluoro(methyl vinyl)ether (PMVE), andperfluoro-8(cyano-5-methyl-3,6-dioxa-1-octene) (8CNVE) is prepared asfollows: three aqueous streams are each fed continuously to a 1 litermechanically stirred, water jacketed, stainless steel autoclave at arate of 81 cc/hr. The first stream consisted of 2.7 g ammoniumpersulfate and 35.3 g of disodium phosphate heptahydrate per liter ofdeionized water. The second consisted of 11.25 g of the HFPO dimer acidper liter of deionized water. The third stream consisted of 13.2 g ofthe 21.4 wt % aqueous dispersion of fluorinated ionomer particulatedescribed above per liter of deionized water. Using a diaphragmcompressor, a mixture of TFE (56.3 g/hr) and PMVE (68.6 g/hr) is fed atconstant rate. The liquid monomer, 8CNVE, is fed separately at a rate of3.4 g/hr. The temperature is maintained at 85° C., the pressure at 4.1MPa (600 psi), and the pH at 6.3 throughout the reaction. The polymeremulsion is removed continuously by means of a letdown valve and theunreacted monomers are vented. The polymer is isolated from the emulsionby first diluting it with deionized water at the rate of 8 literdeionized water per liter of emulsion, followed by addition of 320 cc ofa magnesium sulfate solution (100 g magnesium sulfate heptahydrate perliter of deionized water) per liter of emulsion at a temperature of 60°C. The resulting slurry is filtered, and the polymer solids obtainedfrom a liter of emulsion are re-dispersed in 8 liters of deionized waterat 60° C. After filtering, the wet crumb is dried in a forced air ovenfor 48 hr at 70° C. Polymer yield is approximately 103 g per hour ofreactor operation. The wt % of fluorinated ionomer in the dispersionparticles (FI Nucleus) is calculated to be 0.22 wt %. The polymercomposition is 45.1 wt % PMVE, 1.48 wt % 8CNVE, the remainder beingtetrafluoroethylene. The polymer has an inherent viscosity of 0.88measured in a solution of 0.1 g polymer in 100 g of “Flutec” PP-11 (F2Chemicals Ltd., Preston, UK) at 30° C.

Example 8 Perfluoroelastomer Polymerization Using Dispersed FluorinatedIonomer Particulate and Surfactant 11 (SOS)

This example demonstrates the polymerization of a perfluoroelastomer inthe presence of dispersed fluorinated ionomer particulate andhydrocarbon surfactant (Surfactant 11—SOS).

A perfluoroelastomer containing copolymerized monomers oftetrafluoroethylene (TFE), perfluoro(methyl vinyl)ether (PMVE), andperfluoro-8(cyano-5-methyl-3,6-dioxa-1-octene) (8CNVE) is prepared asfollows: three aqueous streams are each fed continuously to a 1 litermechanically stirred, water jacketed, stainless steel autoclave at arate of 81 cc/hr. The first stream consisted of 3.7 g ammoniumpersulfate and 47.1 g of disodium phosphate heptahydrate per liter ofdeionized water. The second consisted of 6.82 g of sodium octylsulfonate(SOS) solution (Witconate NAS-8, 44 wt % aqueous solution of sodiumoctylsulfonate, Akzo Nobel Surfactants, Chicago, Ill.) per liter ofdeionized water. The third stream consisted of 13.2 g of the 21.4 wt %aqueous dispersion of fluorinated ionomer particulate described aboveper liter of deionized water. Using a diaphragm compressor, a mixture ofTFE (56.3 g/hr) and PMVE (68.6 g/hr) is fed at constant rate. The liquidmonomer, 8CNVE, is fed separately at a rate of 3.4 g/hr. The temperatureis maintained at 85° C., the pressure at 4.1 MPa (600 psi), and the pHat 6.7 throughout the reaction. The polymer emulsion is removedcontinuously by means of a letdown valve and the unreacted monomers arevented. The polymer is isolated from the emulsion by first diluting itwith deionized water at the rate of 8 liter deionized water per liter ofemulsion, followed by addition of 320 cc of a magnesium sulfate solution(100 g magnesium sulfate heptahydrate per liter of deionized water) perliter of emulsion at a temperature of 60° C. The resulting slurry isfiltered, and the polymer solids obtained from a liter of emulsion arere-dispersed in 8 liters of deionized water at 60° C. After filtering,the wet crumb is dried in a forced air oven for 48 hr at 70° C. Polymeryield is approximately 85 g per hour of reactor operation. The wt % offluorinated ionomer in the dispersion particles (FI Nucleus) iscalculated to be 0.29 wt %. The polymer composition is 39.5 wt % PMVE,1.50 wt % 8CNVE, the remainder being tetrafluoroethylene. The polymerhad an inherent viscosity of 0.93 measured in a solution of 0.1 gpolymer in 100 g of “Flutec” PP-11 (F2 Chemicals Ltd., Preston, UK) at30° C.

Example 9 Fluoroelastomer Polymerization Using Dispersed FluorinatedIonomer Particulate and Surfactant 2 (DAS)

This example demonstrates the polymerization of a fluoroelastomer in thepresence of dispersed fluorinated ionomer particulate and short chainfluoroether surfactant (Surfactant 2—DAS). A fluoroelastomer containingcopolymerized monomers of vinylidene fluoride (VF2), hexafluoropropylene(HFP) and tetrafluoroethylene (TFE) is prepared in this example.

A solution of 25 liters water, 30 g of C₃F₇OCF(CF₃)COOH, 5 g ammoniumhydroxide, 30 g disodium phosphate heptahydrate, and 11.0 g of the 21.4wt % aqueous dispersion of fluorinated ionomer particulate describedabove is charged to a 40 liter reactor. The solution is heated to 80° C.After removal of trace oxygen, the reactor is pressurized to 2.1 MPawith a mixture of 3.9 wt % vinylidene fluoride (VF2), 86.1 wt %hexafluoropropene (HFP), and 10.0 wt % tetrafluoroethylene (TFE). Thereactor is charged with 50.0 ml of an initiator solution of 1% ammoniumpersulfate and 5% disodium phosphate heptahydrate to startpolymerization. As the reactor pressure dropped, a mixture of 35.0 wt %vinylidene fluoride, 37.1 wt % hexafluoropropene, and 27.9 wt %tetrafluoroethylene is fed to the reactor to maintain a 2.0 MPapressure. After 45 g of this monomer mixture is fed, 26.0 g of a mixtureof 37.29 mol % 1,4-diiodoperfluorobutane, 46.38 mol %1,6-diiodoperfluorohexane, 11.98 mol % 1,8-diiodoperfluorooctane, and3.76 mol % 1,10-diiodoperfluorodecane is charged to the reactor.Additional initiator solution is added to maintain polymerization rate.After 3700 g of the monomer mixture had been added,4-iodo-3,3,4,4-tetrafluorobutene-1 (ITFB) is introduced to the reactorat a feed rate of 5.0 g ITFB per 1000 g monomer. After a total of 8333 gincremental major monomer is fed, corresponding to a total of 198 mlinitiator solution, 20.4 g ITFB and 13 hours, monomer and initiator fedis discontinued. The reactor is cooled and the pressure in the reactoris reduced to atmospheric. The resulting fluoroelastomer latex has asolids content of 23.7 wt. % solids, a pH of 3.4. The latex iscoagulated with aluminum sulfate solution, washed with deionized water,and dried. The fluoroelastomer has an inherent viscosity of 0.52 dl/g, aMooney viscosity, ML (1+10) at 121 C, of 73 and contains 35.6 wt % VF2,34.9 wt % HFP, 29.2 wt % TFE and 0.21 wt % I. The wt % of fluorinatedionomer in the dispersion particles (FI Nucleus) is calculated to be0.028 wt %.

Example 10 Fluoroelastomer Polymerization Using Dispersed FluorinatedIonomer Particulate and Surfactant 11 (SOS)

This example demonstrates the polymerization of a fluoroelastomer in thepresence of dispersed fluorinated ionomer particulate and hydrocarbonsurfactant (Surfactant 11—SOS). A fluoroelastomer containingcopolymerized monomers of ethylene (E), tetrafluoroethylene (TFE) andperfluoro(methyl vinyl)ether (PMVE) is prepared in this example.

A solution of 25.5 g disodium phosphate heptahydrate, 12.0 g of the 21.4wt % aqueous dispersion of fluorinated ionomer particulate describedabove, and 27 liters of deionized, deoxygenated water is prepared, and25 liters of this solution is charged to a 40 liter reactor. Thesolution is heated to 80° C. After removal of trace oxygen, the reactoris pressurized to 2.1 MPa with a mixture of 30 wt % tetrafluoroethylene(TFE) and 70 wt % perfluoromethylvinylether (PMVE). The reactor ischarged with 55.0 ml of an initiator solution of 1% ammonium persulfateand 0.35 wt % sodium hydroxide to start polymerization. As the reactorpressure drops, a mixture of 7.7 wt % ethylene (E), 44.3 wt % TFE, and47.9 wt % PMVE is fed to the reactor to maintain a 2.1 MPa pressure.After 90 g of this monomer mixture is fed, 28.0 g of a mixture of 37.29mol % 1,4-diiodoperfluorobutane, 46.38 mol % 1,6-diiodoperfluorohexane,11.98 mol % 1,8-diiodoperfluorooctane, and 3.76 mol %1,10-diiodoperfluorodecane is charged to the reactor. Additionalinitiator solution is added to maintain polymerization rate. After 800 gof monomer mixture is fed, an aqueous solution of sodium octylsulfonate(SOS) (10 wt % SOS) is fed to the reactor at a feed rate of 60 ml per3000 g monomer. After 7000 g of the monomer mixture had been added, SOSfeed is stopped. After a total of 8696 g incremental major monomer isfed, corresponding to a total of 745 ml initiator solution and 26 hours,monomer and initiator fed is discontinued. The reactor is cooled and thepressure in the reactor reduced to atmospheric. The resultingfluoroelastomer latex has a solids content of 18 wt. % solids, and a pHof 3.4. The latex is coagulated with aluminum sulfate solution, washedwith deionized water, and dried. The fluoroelastomer has a Mooneyviscosity, ML (1+10) at 121 C, of 74 and contains 46.2 wt % TFE, 42.2PMVE, 11.4 wt % E, and 0.18 wt % I. The wt % of fluorinated ionomer inthe dispersion particles (FI Nucleus) is calculated to be 0.03 wt %.

Example 11 Perfluoroelastomer Polymerization Using Dispersed ModifiedFluorinated Ionomer Particulate and Surfactant 12 (HFPO Dimer PhosphateEster)

This example demonstrates the polymerization of a perfluoroelastomer ina continuous stirred reactor in the presence of a dispersed modifiedfluorinated ionomer particulate and a fluorosurfactant (Surfactant12—HFPO Dimer Phosphate Ester).

The fluorinated ionomer particulate is modified by the followingprocedure. A solution of 1850 g water, 32.2 g of Surfactant 12(C₃F₇OCF(CF₃)—CH₂—O—PO(OH)O⁻NH₄ ⁺) and 45 ml of the 21.4 wt % aqueousdispersion of fluorinated ionomer particulate described above is chargedto a 3.79 liter reactor. The solution is heated to 75° C. After removalof trace oxygen, the reactor is pressurized to 2.07 MPa with a mixtureof perfluoro(methyl vinyl)ether (PMVE) and tetrafluoroethylene (TFE) ina ratio of 55/45 by weight. The reactor is charged with 105.7 ml of a 1wt % ammonium persulfate initiator solution and then 1.01 ml/minute ofthe initiator solution is fed to the reactor until 50 g total of TFE andPMVE has been consumed. During the reaction, the reactor is charged witha mixture of perfluoro(methyl vinyl)ether (PMVE) and tetrafluoroethylene(TFE) in a ratio of 55/45 by weight in order to maintain the reactorpressure at 2.07 MPa. The resulting dispersion of modified fluorinatedionomer particulate contains 5.08 wt % solids. The weight averagediameter of the modified particulate is 34.2 nm (vs. 5.23 nm diameter ofthe original particulate). In addition to the copolymerized TFE/PMVEcoating, this increase in particulate size implies some agglomeration.

A perfluoroelastomer containing copolymerized monomers oftetrafluoroethylene (TFE), perfluoro(methyl vinyl)ether (PMVE), andperfluoro-8(cyano-5-methyl-3,6-dioxa-1-octene) (8CNVE) is prepared asfollows: three aqueous streams are each fed continuously to a 1 litermechanically stirred, water jacketed, stainless steel autoclave. Thefirst stream, fed at a rate of 95 milliliters per hour (ml/hr), consistsof 1.93 g ammonium persulfate and 6.93 g of disodium phosphateheptahydrate per liter of deionized water. The second stream, fed at arate of 81 ml/hr, consists of 30 g of Surfactant 12(C₃F₇OCF(CF₃)—CH₂—O—PO(OH)O⁻NH₄ ⁺) per liter of deionized water. Thethird stream, fed at a rate of 67 ml/hr, consists of a 5.08 wt % aqueousdispersion of the modified fluorinated ionomer particulate preparedabove. Using a diaphragm compressor, a mixture of TFE (56.3 g/hr) andPMVE (68.6 g/hr) is fed at constant rate. The liquid monomer, 8CNVE, isfed separately at a rate of 3.4 g/hr. The temperature is maintained at85° C., the pressure at 4.1 MPa (600 psi), and the pH at 3.5 throughoutthe reaction. The polymer emulsion is removed continuously by means of aletdown valve and the unreacted monomers were vented. The polymer isisolated from the emulsion by first diluting it with deionized water atthe rate of 8 liters deionized water per liter of emulsion, followed byaddition of 530 cc of a magnesium sulfate solution (100 g magnesiumsulfate heptahydrate per liter of deionized water) per liter of emulsionat a temperature of 60° C. The resulting slurry is filtered, and thepolymer solids obtained from a liter of emulsion were re-dispersed in 8liters of deionized water at 60° C. After filtering, the wet crumb isdried in a forced air oven for 48 hr at 70° C. Polymer yield isapproximately 133 g per hour of reactor operation. The wt % offluorinated ionomer in the dispersion particles (FI Nucleus) iscalculated to be 0.0026 wt %. The polymer composition is 49.6 wt % PMVE,2.34 wt % 8CNVE, the remainder being tetrafluoroethylene. The polymerhas an inherent viscosity of 0.75 measured in a solution of 0.1 gpolymer in 100 g of Flutec PP-11 (F2 Chemicals Ltd., Preston, UK) at 30°C.

What is claimed is:
 1. A process for making an aqueous dispersion offluoropolymer particles comprising: providing dispersed solidparticulate of fluorinated ionomer in an aqueous polymerization medium;polymerizing at least one fluorinated monomer in said aqueouspolymerization medium in the presence of said dispersed particulate offluorinated ionomer and initiator to form the aqueous dispersion ofparticles of fluoropolymer, said fluoropolymer being nonionomericfluoropolymer, wherein the amount of said dispersed particulate offluorinated ionomer provided in said aqueous polymerization mediumcomprises less than about 1 wt % of said fluoropolymer solids producedin said aqueous dispersion.
 2. The process of claim 1 wherein saiddispersed particulate of fluorinated ionomer has a weight averageparticle size of about 2 nm to about 100 nm.
 3. The process of claim 1wherein said fluorinated ionomer has an ion exchange ratio of about 3 toabout
 53. 4. The process of claim 1 wherein said fluorinated ionomer ishighly fluorinated.
 5. The process of claim 1 wherein said fluorinatedionomer is perfluorinated.
 6. The process of claim 1 wherein saidfluorinated ionomer comprises a polymer backbone with recurring sidechains attached to the polymer backbone with the side chains carryingionic groups.
 7. The process of claim 1 wherein said fluorinated ionomercomprises ionic groups having a pKa less than about
 10. 8. The processof claim 1 wherein said fluorinated ionomer comprises ionic groupsselected from the group consisting of sulfonate, carboxylate,phosphonate, phosphate, and mixtures thereof.
 9. The process of claim 1wherein said fluorinated ionomer comprises sulfonate groups.
 10. Theprocess of claim 6 wherein said recurring side chains are represented bythe formula—(O—CF₂CFR_(f))_(a)—(O—CF₂)_(b)—(CFR′_(f))_(c)SO₃X, wherein R_(f) andR′_(f) are independently selected from F, Cl or a perfluorinated alkylgroup having 1 to 10 carbon atoms, a=0 to 2, b=0 to 1, c=0 to 6, and Xis H, Li, Na, K or NH₄.
 11. The process of claim 10 wherein saidrecurring side chain is represented by the formula—O—CF₂CF(CF₃)—O—CF₂CF₂SO₃X is H, Li, Na, K or NH₄.
 12. The process ofclaim 1 wherein said fluorinated ionomer in thermoplastic form has amelt flow at 270° C. using a 5 kg weight of about 1 to about
 500. 13.The process of claim 1 further comprising providing surfactant in saidpolymerization medium.
 14. The process of claim 1 further comprisingproviding fluorosurfactant in said polymerization medium.
 15. Theprocess of claim 1 further comprising providing fluoroether surfactantin said polymerization medium.
 16. The process of claim 15 wherein saidfluorosurfactant has the formula:[R¹—O_(n)-L-A⁻]Y⁺ wherein: R¹ is a linear or branched partially or fullyfluorinated aliphatic group which may contain ether linkages; n is 0 or1; L is a linear or branched alkylene group which may be nonfluorinated,partially fluorinated or fully fluorinated and which may contain etherlinkages; A⁻is an anionic group selected from the group consisting ofcarboxylate, sulfonate, sulfonamide anion, and phosphonate; and Y⁺ishydrogen, ammonium or alkali metal cation; with the proviso that thechain length of R¹—O_(n)-L- is not greater than 6 atoms.
 17. The processof claim 16 wherein n is
 1. 18. The process of claim 17 wherein R¹ isCF₃CF₂CF₂—; L is —CF(CF₃)—; and A⁻is carboxylate; and Y⁺is hydrogen orammonium.
 19. The process of claim 1 wherein said aqueous mediumcontains less than about 300 ppm of perfluoroalkane carboxylic acid orsalt fluorosurfactant having 8 or more carbon atoms based on the weightof water in said aqueous polymerization medium.
 20. The process of claim1 wherein said polymerizing produces less than about 13 wt % undispersedfluoropolymer based on the total weight of fluoropolymer produced. 21.The process of claim 1 wherein said at least one fluorinated monomer isselected from the group consisting of tetrafluoroethylene (TFE),hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE),trifluoroethylene, hexafluoroisobutylene, perfluoroalkyl ethylenes,fluorovinyl ethers, vinyl fluoride (VF), vinylidene fluoride (VF2),perfluoro-2,2-dimethyl-1,3-dioxole (PDD), perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD), perfluoro(allyl vinyl ether) andperfluoro(butenyl vinyl ether).
 22. The process of claim 1 wherein saidpolymerizing of said at least one fluorinated monomer producespolytetrafluoroethylene or modified polytetrafluoroethylene having acomonomer content of no greater than about 1 wt %.
 23. The process ofclaim 1 wherein said polymerizing of said at least one fluorinatedmonomer produces a melt-processible copolymer comprising at least about60-98 wt % tetrafluoroethylene units and about 2-40 wt % of at least oneother monomer.
 24. The process of claim 1 wherein said polymerizing ofsaid at least one fluorinated monomer produces a melt-processiblecopolymer containing functional groups which are precursors for ionicgroups.
 25. The process of claim 1 wherein said polymerizing of said atleast one fluorinated monomer produces a fluorocarbon elastomer.
 26. Theprocess of claim 25 wherein said fluorocarbon elastomer copolymerscomprise 25 to 70 wt %, based on total weight of the fluorocarbonelastomer, of copolymerized units of a first fluorinated monomerselected from the group consisting of vinylidene fluoride (VF2),tetrafluoroethylene (TFE), and mixtures thereof.
 27. The process ofclaim 1 wherein providing said dispersed fluorinated ionomer particulatein said aqueous polymerization medium is performed by mixing aconcentrated aqueous dispersion or dispersible powder of saidfluorinated ionomer into said aqueous polymerization medium.